<?xml version="1.0" encoding="us-ascii"?>
<!-- DFIN ActiveDisclosure(SM) XBRL Linkbase Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2020-10-26T22:04:46.0877075+00:00 -->
<!-- Version            : 5.0.1.513 -->
<!-- Package ID         : 55466a7cbb5c4b18bc99ba4cc4872168 -->
<!-- Copyright (c) 2020 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" arcroleURI="http://xbrl.org/int/dim/arcrole/all" />
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" />
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" />
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" />
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" />
  <link:roleRef xlink:type="simple" xlink:href="fmao-20200930.xsd#TemplateLink" roleURI="http://www.fm.bank/20200930/role/TemplateLink" />
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/StatementCondensedConsolidatedStatementsOfIncomeUnaudited" xlink:href="fmao-20200930.xsd#Role_StatementCondensedConsolidatedStatementsOfIncomeUnaudited" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/StatementCondensedConsolidatedStatementsOfIncomeUnaudited">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockDividendsPerShareDeclared" xlink:type="locator" xlink:label="us-gaap_CommonStockDividendsPerShareDeclared" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EarningsPerShareBasicAndDiluted" xlink:type="locator" xlink:label="us-gaap_EarningsPerShareBasicAndDiluted" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLoss" xlink:type="locator" xlink:label="us-gaap_NetIncomeLoss" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:type="locator" xlink:label="us-gaap_IncomeTaxExpenseBenefit" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:type="locator" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NoninterestExpense" xlink:type="locator" xlink:label="us-gaap_NoninterestExpense" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SellingGeneralAndAdministrativeExpense" xlink:type="locator" xlink:label="us-gaap_SellingGeneralAndAdministrativeExpense" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProfessionalFees" xlink:type="locator" xlink:label="us-gaap_ProfessionalFees" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AmortizationOfMortgageServicingRightsMSRs" xlink:type="locator" xlink:label="us-gaap_AmortizationOfMortgageServicingRightsMSRs" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FederalDepositInsuranceCorporationPremiumExpense" xlink:type="locator" xlink:label="us-gaap_FederalDepositInsuranceCorporationPremiumExpense" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GainLossOnSaleOfOtherAssets" xlink:type="locator" xlink:label="us-gaap_GainLossOnSaleOfOtherAssets" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdvertisingExpense" xlink:type="locator" xlink:label="us-gaap_AdvertisingExpense" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AtmExpense" xlink:type="locator" xlink:label="fmao_AtmExpense" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TaxesExcludingIncomeAndExciseTaxes" xlink:type="locator" xlink:label="us-gaap_TaxesExcludingIncomeAndExciseTaxes" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InformationTechnologyAndDataProcessing" xlink:type="locator" xlink:label="us-gaap_InformationTechnologyAndDataProcessing" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquipmentExpense" xlink:type="locator" xlink:label="us-gaap_EquipmentExpense" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OccupancyNet" xlink:type="locator" xlink:label="us-gaap_OccupancyNet" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeBenefitsAndShareBasedCompensation" xlink:type="locator" xlink:label="us-gaap_EmployeeBenefitsAndShareBasedCompensation" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SalariesAndWages" xlink:type="locator" xlink:label="us-gaap_SalariesAndWages" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NoninterestExpenseAbstract" xlink:type="locator" xlink:label="us-gaap_NoninterestExpenseAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NoninterestIncome" xlink:type="locator" xlink:label="us-gaap_NoninterestIncome" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleRealizedGainLoss" xlink:type="locator" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleRealizedGainLoss" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GainLossOnSalesOfLoansNet" xlink:type="locator" xlink:label="us-gaap_GainLossOnSalesOfLoansNet" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:type="locator" xlink:label="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NoninterestIncomeAbstract" xlink:type="locator" xlink:label="us-gaap_NoninterestIncomeAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss" xlink:type="locator" xlink:label="us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProvisionForLoanAndLeaseLosses" xlink:type="locator" xlink:label="us-gaap_ProvisionForLoanAndLeaseLosses" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestIncomeExpenseNet" xlink:type="locator" xlink:label="us-gaap_InterestIncomeExpenseNet" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestExpense" xlink:type="locator" xlink:label="us-gaap_InterestExpense" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestExpenseFederalHomeLoanBankAndFederalReserveBankAdvancesLongTerm" xlink:type="locator" xlink:label="us-gaap_InterestExpenseFederalHomeLoanBankAndFederalReserveBankAdvancesLongTerm" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestExpenseFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase" xlink:type="locator" xlink:label="us-gaap_InterestExpenseFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestExpenseDeposits" xlink:type="locator" xlink:label="us-gaap_InterestExpenseDeposits" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestExpenseAbstract" xlink:type="locator" xlink:label="us-gaap_InterestExpenseAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestAndDividendIncomeOperating" xlink:type="locator" xlink:label="us-gaap_InterestAndDividendIncomeOperating" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestIncomeOther" xlink:type="locator" xlink:label="us-gaap_InterestIncomeOther" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_InterestIncomeExpenseFederalFundsSoldAndPurchased" xlink:type="locator" xlink:label="fmao_InterestIncomeExpenseFederalFundsSoldAndPurchased" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DividendIncomeOperating" xlink:type="locator" xlink:label="us-gaap_DividendIncomeOperating" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestIncomeSecuritiesStateAndMunicipal" xlink:type="locator" xlink:label="us-gaap_InterestIncomeSecuritiesStateAndMunicipal" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestIncomeSecuritiesUSTreasuryAndOtherUSGovernment" xlink:type="locator" xlink:label="us-gaap_InterestIncomeSecuritiesUSTreasuryAndOtherUSGovernment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestIncomeSecuritiesBySecurityTypeAbstract" xlink:type="locator" xlink:label="us-gaap_InterestIncomeSecuritiesBySecurityTypeAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestAndFeeIncomeLoansAndLeases" xlink:type="locator" xlink:label="us-gaap_InterestAndFeeIncomeLoansAndLeases" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:type="locator" xlink:label="us-gaap_InterestAndDividendIncomeOperatingAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialServiceOtherMember" xlink:type="locator" xlink:label="us-gaap_FinancialServiceOtherMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BankServicingMember" xlink:type="locator" xlink:label="us-gaap_BankServicingMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain" xlink:type="locator" xlink:label="srt_ProductsAndServicesDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain" xlink:type="locator" xlink:label="srt_ProductsAndServicesDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductOrServiceAxis" xlink:type="locator" xlink:label="srt_ProductOrServiceAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:type="locator" xlink:label="us-gaap_StatementTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:type="locator" xlink:label="us-gaap_StatementLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" order="10360.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_ProductOrServiceAxis" order="10390.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain_2" order="10400.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" order="10420.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="us-gaap_BankServicingMember" order="10440.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="us-gaap_FinancialServiceOtherMember" order="10460.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InterestAndDividendIncomeOperatingAbstract" order="10490.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:to="us-gaap_InterestAndFeeIncomeLoansAndLeases" order="10650.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:to="us-gaap_InterestIncomeSecuritiesBySecurityTypeAbstract" order="10730.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestIncomeSecuritiesBySecurityTypeAbstract" xlink:to="us-gaap_InterestIncomeSecuritiesUSTreasuryAndOtherUSGovernment" order="10890.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestIncomeSecuritiesBySecurityTypeAbstract" xlink:to="us-gaap_InterestIncomeSecuritiesStateAndMunicipal" order="10970.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:to="us-gaap_DividendIncomeOperating" order="11050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:to="fmao_InterestIncomeExpenseFederalFundsSoldAndPurchased" order="11130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:to="us-gaap_InterestIncomeOther" order="11210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:to="us-gaap_InterestAndDividendIncomeOperating" order="11290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InterestExpenseAbstract" order="11370.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestExpenseAbstract" xlink:to="us-gaap_InterestExpenseDeposits" order="11530.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestExpenseAbstract" xlink:to="us-gaap_InterestExpenseFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase" order="11610.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestExpenseAbstract" xlink:to="us-gaap_InterestExpenseFederalHomeLoanBankAndFederalReserveBankAdvancesLongTerm" order="11690.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InterestExpenseAbstract" xlink:to="us-gaap_InterestExpense" order="11770.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InterestIncomeExpenseNet" order="11850.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ProvisionForLoanAndLeaseLosses" order="11930.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss" order="12010.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NoninterestIncomeAbstract" order="12090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestIncomeAbstract" xlink:to="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" order="12250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestIncomeAbstract" xlink:to="us-gaap_GainLossOnSalesOfLoansNet" order="12410.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestIncomeAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleRealizedGainLoss" order="12490.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestIncomeAbstract" xlink:to="us-gaap_NoninterestIncome" order="12570.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NoninterestExpenseAbstract" order="12650.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_SalariesAndWages" order="12810.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_EmployeeBenefitsAndShareBasedCompensation" order="12890.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_OccupancyNet" order="12970.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_EquipmentExpense" order="13050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_InformationTechnologyAndDataProcessing" order="13130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_TaxesExcludingIncomeAndExciseTaxes" order="13210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="fmao_AtmExpense" order="13290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_AdvertisingExpense" order="13370.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_GainLossOnSaleOfOtherAssets" order="13450.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_FederalDepositInsuranceCorporationPremiumExpense" order="13530.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_AmortizationOfMortgageServicingRightsMSRs" order="13610.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_ProfessionalFees" order="13690.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_SellingGeneralAndAdministrativeExpense" order="13770.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoninterestExpenseAbstract" xlink:to="us-gaap_NoninterestExpense" order="13850.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" order="13930.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncomeTaxExpenseBenefit" order="14010.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetIncomeLoss" order="14090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EarningsPerShareBasicAndDiluted" order="14170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockDividendsPerShareDeclared" order="14250.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/StatementCondensedConsolidatedStatementsOfChangesToStockholderSEquityUnaudited" xlink:href="fmao-20200930.xsd#Role_StatementCondensedConsolidatedStatementsOfChangesToStockholderSEquityUnaudited" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/StatementCondensedConsolidatedStatementsOfChangesToStockholderSEquityUnaudited">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DividendsCommonStockCash" xlink:type="locator" xlink:label="us-gaap_DividendsCommonStockCash" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_StockIssuedDuringPeriodSharesDirectorStockAward" xlink:type="locator" xlink:label="fmao_StockIssuedDuringPeriodSharesDirectorStockAward" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_StockIssuedDuringPeriodValueDirectorStockAward" xlink:type="locator" xlink:label="fmao_StockIssuedDuringPeriodValueDirectorStockAward" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TreasuryStockSharesAcquired" xlink:type="locator" xlink:label="us-gaap_TreasuryStockSharesAcquired" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:type="locator" xlink:label="us-gaap_TreasuryStockValueAcquiredCostMethod" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodSharesAcquisitions" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueAcquisitions" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodValueAcquisitions" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:type="locator" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLoss" xlink:type="locator" xlink:label="us-gaap_NetIncomeLoss" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharesIssued" xlink:type="locator" xlink:label="us-gaap_SharesIssued" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquity" xlink:type="locator" xlink:label="us-gaap_StockholdersEquity" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:type="locator" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:type="locator" xlink:label="us-gaap_RetainedEarningsMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TreasuryStockMember" xlink:type="locator" xlink:label="us-gaap_TreasuryStockMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockMember" xlink:type="locator" xlink:label="us-gaap_CommonStockMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain" xlink:type="locator" xlink:label="us-gaap_EquityComponentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain" xlink:type="locator" xlink:label="us-gaap_EquityComponentDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:type="locator" xlink:label="us-gaap_StatementEquityComponentsAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:type="locator" xlink:label="us-gaap_StatementTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:type="locator" xlink:label="us-gaap_StatementLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementEquityComponentsAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain_2" order="10050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_TreasuryStockMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_RetainedEarningsMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockholdersEquity" order="10340.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SharesIssued" order="10360.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetIncomeLoss" order="10480.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherComprehensiveIncomeLossNetOfTax" order="10620.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueAcquisitions" order="10760.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesAcquisitions" order="10780.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TreasuryStockValueAcquiredCostMethod" order="10900.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_TreasuryStockSharesAcquired" order="10920.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures" order="11040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures" order="11060.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" order="11320.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="fmao_StockIssuedDuringPeriodValueDirectorStockAward" order="11460.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="fmao_StockIssuedDuringPeriodSharesDirectorStockAward" order="11480.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DividendsCommonStockCash" order="11600.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/StatementCondensedConsolidatedStatementsOfChangesToStockholderSEquityParentheticalUnaudited" xlink:href="fmao-20200930.xsd#Role_StatementCondensedConsolidatedStatementsOfChangesToStockholderSEquityParentheticalUnaudited" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/StatementCondensedConsolidatedStatementsOfChangesToStockholderSEquityParentheticalUnaudited">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodSharesAcquisitions" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockDividendsPerShareDeclared" xlink:type="locator" xlink:label="us-gaap_CommonStockDividendsPerShareDeclared" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockMember" xlink:type="locator" xlink:label="us-gaap_CommonStockMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain" xlink:type="locator" xlink:label="us-gaap_EquityComponentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:type="locator" xlink:label="us-gaap_StatementEquityComponentsAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:type="locator" xlink:label="us-gaap_StatementTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:type="locator" xlink:label="us-gaap_StatementLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementEquityComponentsAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" order="10160.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited" order="10280.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CommonStockDividendsPerShareDeclared" order="10400.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesAcquisitions" order="10520.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited" xlink:href="fmao-20200930.xsd#Role_StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NoncashOrPartNoncashAcquisitionValueOfLiabilitiesAssumed1" xlink:type="locator" xlink:label="us-gaap_NoncashOrPartNoncashAcquisitionValueOfLiabilitiesAssumed1" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesGross" xlink:type="locator" xlink:label="us-gaap_PaymentsToAcquireBusinessesGross" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssued1" xlink:type="locator" xlink:label="us-gaap_StockIssued1" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueOfAssetsAcquired" xlink:type="locator" xlink:label="us-gaap_FairValueOfAssetsAcquired" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NoncashOrPartNoncashAcquisitionValueOfLiabilitiesAssumedAbstract" xlink:type="locator" xlink:label="us-gaap_NoncashOrPartNoncashAcquisitionValueOfLiabilitiesAssumedAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransferOfOtherRealEstate" xlink:type="locator" xlink:label="us-gaap_TransferOfOtherRealEstate" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherNoncashInvestingAndFinancingItemsAbstract" xlink:type="locator" xlink:label="us-gaap_OtherNoncashInvestingAndFinancingItemsAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeTaxesPaid" xlink:type="locator" xlink:label="us-gaap_IncomeTaxesPaid" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestPaidNet" xlink:type="locator" xlink:label="us-gaap_InterestPaidNet" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_CashPaidDuringPeriodAbstract" xlink:type="locator" xlink:label="fmao_CashPaidDuringPeriodAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:type="locator" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" xlink:type="locator" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" xlink:type="locator" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsOfDividendsCommonStock" xlink:type="locator" xlink:label="us-gaap_PaymentsOfDividendsCommonStock" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:type="locator" xlink:label="us-gaap_PaymentsForRepurchaseOfCommonStock" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RepaymentsOfFederalHomeLoanBankBorrowings" xlink:type="locator" xlink:label="us-gaap_RepaymentsOfFederalHomeLoanBankBorrowings" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchaseNet" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchaseNet" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInDeposits" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInDeposits" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired" xlink:type="locator" xlink:label="us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsForProceedsFromLoansAndLeases" xlink:type="locator" xlink:label="us-gaap_PaymentsForProceedsFromLoansAndLeases" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:type="locator" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromSaleOfProductiveAssets" xlink:type="locator" xlink:label="us-gaap_ProceedsFromSaleOfProductiveAssets" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromPaymentsForInInterestBearingDepositsInBanks" xlink:type="locator" xlink:label="us-gaap_ProceedsFromPaymentsForInInterestBearingDepositsInBanks" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_PaymentsToAcquireSalesOfOtherSecurities" xlink:type="locator" xlink:label="fmao_PaymentsToAcquireSalesOfOtherSecurities" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_ProceedsFromSalesOfOtherSecurities" xlink:type="locator" xlink:label="fmao_ProceedsFromSalesOfOtherSecurities" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_ActivityInOtherSecuritiesAtCostAbstract" xlink:type="locator" xlink:label="fmao_ActivityInOtherSecuritiesAtCostAbstract" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_PaymentsToAcquireAvailableForSaleSecuritiesDebtIncludingAdjustmentForSecuritiesAcquiredInAcquisition" xlink:type="locator" xlink:label="fmao_PaymentsToAcquireAvailableForSaleSecuritiesDebtIncludingAdjustmentForSecuritiesAcquiredInAcquisition" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt" xlink:type="locator" xlink:label="us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" xlink:type="locator" xlink:label="us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdditionalCashFlowElementsInvestingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_AdditionalCashFlowElementsInvestingActivitiesAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet" xlink:type="locator" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleRealizedGainLoss" xlink:type="locator" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleRealizedGainLoss" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GainLossOnSaleOfOtherAssets" xlink:type="locator" xlink:label="us-gaap_GainLossOnSaleOfOtherAssets" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromSaleOfLoansHeldForSale" xlink:type="locator" xlink:label="us-gaap_ProceedsFromSaleOfLoansHeldForSale" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsForOriginationAndPurchasesOfLoansHeldForSale" xlink:type="locator" xlink:label="us-gaap_PaymentsForOriginationAndPurchasesOfLoansHeldForSale" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GainLossOnSalesOfLoansNet" xlink:type="locator" xlink:label="us-gaap_GainLossOnSalesOfLoansNet" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProvisionForLoanAndLeaseLosses" xlink:type="locator" xlink:label="us-gaap_ProvisionForLoanAndLeaseLosses" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit" xlink:type="locator" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefit" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_ShareBasedCompensationDirectorStockAward" xlink:type="locator" xlink:label="fmao_ShareBasedCompensationDirectorStockAward" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:type="locator" xlink:label="us-gaap_ShareBasedCompensation" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AmortizationAccretionOfFairValueAdjustments" xlink:type="locator" xlink:label="fmao_AmortizationAccretionOfFairValueAdjustments" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:type="locator" xlink:label="us-gaap_AmortizationOfIntangibleAssets" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AmortizationOfMortgageServicingRightsMSRs" xlink:type="locator" xlink:label="us-gaap_AmortizationOfMortgageServicingRightsMSRs" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments" xlink:type="locator" xlink:label="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DepreciationNonproduction" xlink:type="locator" xlink:label="us-gaap_DepreciationNonproduction" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProfitLoss" xlink:type="locator" xlink:label="us-gaap_ProfitLoss" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:type="locator" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_LimberlostBancsharesIncMember" xlink:type="locator" xlink:label="fmao_LimberlostBancsharesIncMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:type="locator" xlink:label="us-gaap_StatementTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:type="locator" xlink:label="us-gaap_StatementLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" order="10350.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_BusinessAcquisitionAxis" order="10380.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain_2" order="10390.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" order="10410.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="fmao_LimberlostBancsharesIncMember" order="10430.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" order="10540.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_ProfitLoss" order="10620.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" order="10660.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_DepreciationNonproduction" order="10740.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments" order="10780.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AmortizationOfMortgageServicingRightsMSRs" order="10820.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AmortizationOfIntangibleAssets" order="10860.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="fmao_AmortizationAccretionOfFairValueAdjustments" order="10900.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_ShareBasedCompensation" order="10940.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="fmao_ShareBasedCompensationDirectorStockAward" order="10980.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_DeferredIncomeTaxExpenseBenefit" order="11020.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_ProvisionForLoanAndLeaseLosses" order="11060.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_GainLossOnSalesOfLoansNet" order="11100.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_PaymentsForOriginationAndPurchasesOfLoansHeldForSale" order="11140.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromSaleOfLoansHeldForSale" order="11180.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_GainLossOnSaleOfOtherAssets" order="11220.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleRealizedGainLoss" order="11260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet" order="11300.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities" order="11340.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" order="11380.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_AdditionalCashFlowElementsInvestingActivitiesAbstract" order="11460.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdditionalCashFlowElementsInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" order="11540.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdditionalCashFlowElementsInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt" order="11580.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AdditionalCashFlowElementsInvestingActivitiesAbstract" xlink:to="fmao_PaymentsToAcquireAvailableForSaleSecuritiesDebtIncludingAdjustmentForSecuritiesAcquiredInAcquisition" order="11620.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="fmao_ActivityInOtherSecuritiesAtCostAbstract" order="11660.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_ActivityInOtherSecuritiesAtCostAbstract" xlink:to="fmao_ProceedsFromSalesOfOtherSecurities" order="11740.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_ActivityInOtherSecuritiesAtCostAbstract" xlink:to="fmao_PaymentsToAcquireSalesOfOtherSecurities" order="11780.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromPaymentsForInInterestBearingDepositsInBanks" order="11820.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_ProceedsFromSaleOfProductiveAssets" order="11860.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" order="11900.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsForProceedsFromLoansAndLeases" order="11940.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired" order="11980.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities" order="12020.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" order="12060.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_IncreaseDecreaseInDeposits" order="12140.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_IncreaseDecreaseInFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchaseNet" order="12180.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_RepaymentsOfFederalHomeLoanBankBorrowings" order="12220.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_PaymentsForRepurchaseOfCommonStock" order="12260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_PaymentsOfDividendsCommonStock" order="12300.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities" order="12340.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect" order="12380.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" order="12420.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SupplementalCashFlowInformationAbstract" order="12530.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="fmao_CashPaidDuringPeriodAbstract" order="12610.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_CashPaidDuringPeriodAbstract" xlink:to="us-gaap_InterestPaidNet" order="12690.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_CashPaidDuringPeriodAbstract" xlink:to="us-gaap_IncomeTaxesPaid" order="12730.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherNoncashInvestingAndFinancingItemsAbstract" order="12770.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_OtherNoncashInvestingAndFinancingItemsAbstract" xlink:to="us-gaap_TransferOfOtherRealEstate" order="12850.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NoncashOrPartNoncashAcquisitionValueOfLiabilitiesAssumedAbstract" order="12890.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoncashOrPartNoncashAcquisitionValueOfLiabilitiesAssumedAbstract" xlink:to="us-gaap_FairValueOfAssetsAcquired" order="12970.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoncashOrPartNoncashAcquisitionValueOfLiabilitiesAssumedAbstract" xlink:to="us-gaap_StockIssued1" order="13010.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoncashOrPartNoncashAcquisitionValueOfLiabilitiesAssumedAbstract" xlink:to="us-gaap_PaymentsToAcquireBusinessesGross" order="13050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_NoncashOrPartNoncashAcquisitionValueOfLiabilitiesAssumedAbstract" xlink:to="us-gaap_NoncashOrPartNoncashAcquisitionValueOfLiabilitiesAssumed1" order="13090.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnauditedParenthetical" xlink:href="fmao-20200930.xsd#Role_StatementCondensedConsolidatedStatementsOfCashFlowsUnauditedParenthetical" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnauditedParenthetical">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferred1" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationConsiderationTransferred1" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_LimberlostBancsharesIncMember" xlink:type="locator" xlink:label="fmao_LimberlostBancsharesIncMember" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:type="locator" xlink:label="dei_EntityDomain" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:type="locator" xlink:label="dei_EntityDomain_2" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:type="locator" xlink:label="dei_LegalEntityAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:type="locator" xlink:label="us-gaap_StatementTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:type="locator" xlink:label="us-gaap_StatementLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="dei_LegalEntityAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain_2" order="10050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_EntityDomain" xlink:to="fmao_LimberlostBancsharesIncMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_BusinessCombinationConsiderationTransferred1" order="10120.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureBusinessCombinationAndAssetPurchaseAdditionalInformationDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureBusinessCombinationAndAssetPurchaseAdditionalInformationDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureBusinessCombinationAndAssetPurchaseAdditionalInformationDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:type="locator" xlink:label="us-gaap_AmortizationOfIntangibleAssets" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesFairValueAdjustment" xlink:type="locator" xlink:label="fmao_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesFairValueAdjustment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Goodwill" xlink:type="locator" xlink:label="us-gaap_Goodwill" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinitelivedIntangibleAssetsAcquired1" xlink:type="locator" xlink:label="us-gaap_FinitelivedIntangibleAssetsAcquired1" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesGross" xlink:type="locator" xlink:label="us-gaap_PaymentsToAcquireBusinessesGross" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferred1" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationConsiderationTransferred1" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionSharePrice" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionSharePrice" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:type="locator" xlink:label="us-gaap_CommonStockSharesOutstanding" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_CashConsiderationPayableOnAcquisitionPerShare" xlink:type="locator" xlink:label="fmao_CashConsiderationPayableOnAcquisitionPerShare" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_NumberOfFullServiceOffices" xlink:type="locator" xlink:label="fmao_NumberOfFullServiceOffices" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_CustarMember" xlink:type="locator" xlink:label="fmao_CustarMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_SegmentGeographicalDomain" xlink:type="locator" xlink:label="srt_SegmentGeographicalDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_SegmentGeographicalDomain" xlink:type="locator" xlink:label="srt_SegmentGeographicalDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_StatementGeographicalAxis" xlink:type="locator" xlink:label="srt_StatementGeographicalAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CoreDepositsMember" xlink:type="locator" xlink:label="us-gaap_CoreDepositsMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:type="locator" xlink:label="dei_EntityDomain" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:type="locator" xlink:label="dei_LegalEntityAxis" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_LimberlostBancsharesIncMember" xlink:type="locator" xlink:label="fmao_LimberlostBancsharesIncMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_BankOfGenevaMember" xlink:type="locator" xlink:label="fmao_BankOfGenevaMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_BusinessAcquisitionAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="fmao_BankOfGenevaMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="fmao_LimberlostBancsharesIncMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="dei_LegalEntityAxis" order="10240.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" order="10270.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_EntityDomain" xlink:to="fmao_LimberlostBancsharesIncMember" order="10290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" order="10360.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2" order="10370.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" order="10390.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="us-gaap_CoreDepositsMember" order="10410.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="srt_StatementGeographicalAxis" order="10440.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain_2" order="10450.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain" order="10470.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_SegmentGeographicalDomain" xlink:to="fmao_CustarMember" order="10490.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="fmao_NumberOfFullServiceOffices" order="10620.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" order="10640.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="fmao_CashConsiderationPayableOnAcquisitionPerShare" order="10660.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_CommonStockSharesOutstanding" order="10680.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessAcquisitionSharePrice" order="10700.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationConsiderationTransferred1" order="10720.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_PaymentsToAcquireBusinessesGross" order="10740.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" order="10760.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_FinitelivedIntangibleAssetsAcquired1" order="10830.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1" order="10850.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_Goodwill" order="10870.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="fmao_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesFairValueAdjustment" order="10920.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_AmortizationOfIntangibleAssets" order="11050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear" order="11090.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureBusinessCombinationAndAssetPurchaseSummaryOfConsiderationPaidAndAmountsOfAssetsAcquiredAndLiabilitiesAssumedRecognizedDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureBusinessCombinationAndAssetPurchaseSummaryOfConsiderationPaidAndAmountsOfAssetsAcquiredAndLiabilitiesAssumedRecognizedDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureBusinessCombinationAndAssetPurchaseSummaryOfConsiderationPaidAndAmountsOfAssetsAcquiredAndLiabilitiesAssumedRecognizedDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedExpensesAndOtherLiabilities" xlink:type="locator" xlink:label="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedExpensesAndOtherLiabilities" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFederalHomeLoanBankAdvances" xlink:type="locator" xlink:label="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFederalHomeLoanBankAdvances" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeposits" xlink:type="locator" xlink:label="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeposits" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInterestBearing" xlink:type="locator" xlink:label="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInterestBearing" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoninterestBearing" xlink:type="locator" xlink:label="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoninterestBearing" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDepositsAbstract" xlink:type="locator" xlink:label="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDepositsAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Goodwill" xlink:type="locator" xlink:label="us-gaap_Goodwill" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoansNet" xlink:type="locator" xlink:label="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoansNet" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherSecurities" xlink:type="locator" xlink:label="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherSecurities" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferred1" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationConsiderationTransferred1" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesGross" xlink:type="locator" xlink:label="us-gaap_PaymentsToAcquireBusinessesGross" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_LimberlostBancsharesIncMember" xlink:type="locator" xlink:label="fmao_LimberlostBancsharesIncMember" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:type="locator" xlink:label="dei_EntityDomain" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:type="locator" xlink:label="dei_LegalEntityAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="10150.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="dei_LegalEntityAxis" order="10180.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_EntityDomain" xlink:to="fmao_LimberlostBancsharesIncMember" order="10230.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_PaymentsToAcquireBusinessesGross" order="10260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" order="10280.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationConsiderationTransferred1" order="10300.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" order="10320.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" order="10360.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities" order="10380.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherSecurities" order="10400.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoansNet" order="10420.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" order="10440.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_Goodwill" order="10460.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets" order="10480.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" order="10500.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" order="10520.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDepositsAbstract" order="10560.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDepositsAbstract" xlink:to="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoninterestBearing" order="10600.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDepositsAbstract" xlink:to="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInterestBearing" order="10620.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDepositsAbstract" xlink:to="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeposits" order="10640.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFederalHomeLoanBankAdvances" order="10660.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="fmao_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedExpensesAndOtherLiabilities" order="10680.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" order="10700.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureBusinessCombinationAndAssetPurchaseSummaryOfConsiderationPaidAndAmountsOfAssetsAcquiredAndLiabilitiesAssumedRecognizedParentheticalDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureBusinessCombinationAndAssetPurchaseSummaryOfConsiderationPaidAndAmountsOfAssetsAcquiredAndLiabilitiesAssumedRecognizedParentheticalDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureBusinessCombinationAndAssetPurchaseSummaryOfConsiderationPaidAndAmountsOfAssetsAcquiredAndLiabilitiesAssumedRecognizedParentheticalDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_LimberlostBancsharesIncMember" xlink:type="locator" xlink:label="fmao_LimberlostBancsharesIncMember" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:type="locator" xlink:label="dei_EntityDomain" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:type="locator" xlink:label="dei_LegalEntityAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="dei_LegalEntityAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="dei_LegalEntityAxis" xlink:to="dei_EntityDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="dei_EntityDomain" xlink:to="fmao_LimberlostBancsharesIncMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" order="10120.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureBusinessCombinationAndAssetPurchaseSummaryOfCarryingAmountOfLoansDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureBusinessCombinationAndAssetPurchaseSummaryOfCarryingAmountOfLoansDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureBusinessCombinationAndAssetPurchaseSummaryOfCarryingAmountOfLoansDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet" xlink:type="locator" xlink:label="us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConsumerLoanMember" xlink:type="locator" xlink:label="us-gaap_ConsumerLoanMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_ConsumerRealEstateLoanMember" xlink:type="locator" xlink:label="fmao_ConsumerRealEstateLoanMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialLoanMember" xlink:type="locator" xlink:label="us-gaap_CommercialLoanMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:type="locator" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_FinancialInstrumentAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" order="10050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_CommercialLoanMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="fmao_ConsumerRealEstateLoanMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_ConsumerLoanMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet" order="10280.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureBusinessCombinationAndAssetPurchaseSummaryOfLoansAcquiredAndContractuallyRequiredPaymentsReceivableDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureBusinessCombinationAndAssetPurchaseSummaryOfLoansAcquiredAndContractuallyRequiredPaymentsReceivableDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureBusinessCombinationAndAssetPurchaseSummaryOfLoansAcquiredAndContractuallyRequiredPaymentsReceivableDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodAtAcquisitionAtFairValue" xlink:type="locator" xlink:label="us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodAtAcquisitionAtFairValue" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodCashFlowsExpectedToBeCollectedAtAcquisition" xlink:type="locator" xlink:label="us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodCashFlowsExpectedToBeCollectedAtAcquisition" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractuallyRequiredPaymentsReceivableAtAcquisition" xlink:type="locator" xlink:label="us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractuallyRequiredPaymentsReceivableAtAcquisition" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConsumerLoanMember" xlink:type="locator" xlink:label="us-gaap_ConsumerLoanMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_ConsumerRealEstateLoanMember" xlink:type="locator" xlink:label="fmao_ConsumerRealEstateLoanMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialLoanMember" xlink:type="locator" xlink:label="us-gaap_CommercialLoanMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:type="locator" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_FinancialInstrumentAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_CommercialLoanMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="fmao_ConsumerRealEstateLoanMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_ConsumerLoanMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractuallyRequiredPaymentsReceivableAtAcquisition" order="10160.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodCashFlowsExpectedToBeCollectedAtAcquisition" order="10240.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAcquiredDuringPeriodAtAcquisitionAtFairValue" order="10260.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureBusinessCombinationAndAssetPurchaseScheduleOfAnnualAmortizationOfCoreDepositIntangibleAssetsDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureBusinessCombinationAndAssetPurchaseScheduleOfAnnualAmortizationOfCoreDepositIntangibleAssetsDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureBusinessCombinationAndAssetPurchaseScheduleOfAnnualAmortizationOfCoreDepositIntangibleAssetsDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_GenevaMember" xlink:type="locator" xlink:label="fmao_GenevaMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_CustarMember" xlink:type="locator" xlink:label="fmao_CustarMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" order="10070.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_BusinessAcquisitionAxis" order="10100.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="fmao_CustarMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="fmao_GenevaMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear" order="10200.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" order="10260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" order="10320.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" order="10380.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" order="10440.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive" order="10500.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsNet" order="10560.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureSecuritiesAmortizedCostAndFairValueOfSecuritiesWithGrossUnrealizedGainsAndLossesDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureSecuritiesAmortizedCostAndFairValueOfSecuritiesWithGrossUnrealizedGainsAndLossesDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureSecuritiesAmortizedCostAndFairValueOfSecuritiesWithGrossUnrealizedGainsAndLossesDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember" xlink:type="locator" xlink:label="us-gaap_USStatesAndPoliticalSubdivisionsMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:type="locator" xlink:label="us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:type="locator" xlink:label="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_USTreasurySecuritiesMember" xlink:type="locator" xlink:label="us-gaap_USTreasurySecuritiesMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:type="locator" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" order="10040.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:to="us-gaap_FinancialInstrumentAxis" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="10100.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USTreasurySecuritiesMember" order="10120.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" order="10140.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" order="10160.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USStatesAndPoliticalSubdivisionsMember" order="10180.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" order="10330.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" order="10530.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" order="10730.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecurities" order="10930.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureSecuritiesAdditionalInformationDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureSecuritiesAdditionalInformationDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureSecuritiesAdditionalInformationDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherInvestmentsAndSecuritiesAtCost" xlink:type="locator" xlink:label="us-gaap_OtherInvestmentsAndSecuritiesAtCost" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged" xlink:type="locator" xlink:label="us-gaap_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_ForUnderWaterSecuritiesLossPositionExpirationPeriod" xlink:type="locator" xlink:label="fmao_ForUnderWaterSecuritiesLossPositionExpirationPeriod" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_MaturityPeriodForUnderWaterSecurities" xlink:type="locator" xlink:label="fmao_MaturityPeriodForUnderWaterSecurities" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_OhioEquityFundForHousingLimitedPartnershipMember" xlink:type="locator" xlink:label="fmao_OhioEquityFundForHousingLimitedPartnershipMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_FederalHomeLoanBankOfCincinnatiAndIndianapolisStockMember" xlink:type="locator" xlink:label="fmao_FederalHomeLoanBankOfCincinnatiAndIndianapolisStockMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:type="locator" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember" xlink:type="locator" xlink:label="srt_MaximumMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MinimumMember" xlink:type="locator" xlink:label="srt_MinimumMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:type="locator" xlink:label="srt_RangeMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:type="locator" xlink:label="srt_RangeMember_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis" xlink:type="locator" xlink:label="srt_RangeAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:to="srt_RangeAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember_2" order="10050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:to="us-gaap_FinancialInstrumentAxis" order="10140.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="fmao_FederalHomeLoanBankOfCincinnatiAndIndianapolisStockMember" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="fmao_OhioEquityFundForHousingLimitedPartnershipMember" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="fmao_MaturityPeriodForUnderWaterSecurities" order="10240.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="fmao_ForUnderWaterSecuritiesLossPositionExpirationPeriod" order="10260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged" order="10310.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_OtherInvestmentsAndSecuritiesAtCost" order="10380.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureSecuritiesGrossUnrealizedLossesAggregatedByInvestmentCategoryAndLengthOfTimeDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureSecuritiesGrossUnrealizedLossesAggregatedByInvestmentCategoryAndLengthOfTimeDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureSecuritiesGrossUnrealizedLossesAggregatedByInvestmentCategoryAndLengthOfTimeDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:type="locator" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:type="locator" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger" xlink:type="locator" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" xlink:type="locator" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months" xlink:type="locator" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" xlink:type="locator" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember" xlink:type="locator" xlink:label="us-gaap_USStatesAndPoliticalSubdivisionsMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:type="locator" xlink:label="us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:type="locator" xlink:label="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_USTreasurySecuritiesMember" xlink:type="locator" xlink:label="us-gaap_USTreasurySecuritiesMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:type="locator" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" order="10050.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:to="us-gaap_FinancialInstrumentAxis" order="10080.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USTreasurySecuritiesMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USStatesAndPoliticalSubdivisionsMember" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" order="10340.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months" order="10540.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" order="10740.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger" order="10940.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" order="11140.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" order="11340.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansLoansDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureLoansLoansDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansLoansDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetReportedAmount" xlink:type="locator" xlink:label="us-gaap_LoansAndLeasesReceivableNetReportedAmount" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansAndLeasesReceivableAllowance" xlink:type="locator" xlink:label="us-gaap_LoansAndLeasesReceivableAllowance" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="locator" xlink:label="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UnamortizedLoanCommitmentAndOriginationFeesAndUnamortizedDiscountsOrPremiums" xlink:type="locator" xlink:label="us-gaap_UnamortizedLoanCommitmentAndOriginationFeesAndUnamortizedDiscountsOrPremiums" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansAndLeasesReceivableGrossCarryingAmount" xlink:type="locator" xlink:label="us-gaap_LoansAndLeasesReceivableGrossCarryingAmount" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableGrossAllowanceAndNetAbstract" xlink:type="locator" xlink:label="us-gaap_AccountsNotesLoansAndFinancingReceivableGrossAllowanceAndNetAbstract" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_OtherLoanMember" xlink:type="locator" xlink:label="fmao_OtherLoanMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_ConsumerPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialRealEstatePortfolioSegmentMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgriculturalLoanMember" xlink:type="locator" xlink:label="fmao_AgriculturalLoanMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgricultureRealEstateMember" xlink:type="locator" xlink:label="fmao_AgricultureRealEstateMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ResidentialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_ResidentialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:type="locator" xlink:label="us-gaap_AccountsNotesAndLoansReceivableLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" order="10050.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" order="10080.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain_2" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ResidentialPortfolioSegmentMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgricultureRealEstateMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgriculturalLoanMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialRealEstatePortfolioSegmentMember" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ConsumerPortfolioSegmentMember" order="10230.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_OtherLoanMember" order="10250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_AccountsNotesLoansAndFinancingReceivableGrossAllowanceAndNetAbstract" order="10280.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesLoansAndFinancingReceivableGrossAllowanceAndNetAbstract" xlink:to="us-gaap_LoansAndLeasesReceivableGrossCarryingAmount" order="10360.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesLoansAndFinancingReceivableGrossAllowanceAndNetAbstract" xlink:to="us-gaap_UnamortizedLoanCommitmentAndOriginationFeesAndUnamortizedDiscountsOrPremiums" order="10680.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesLoansAndFinancingReceivableGrossAllowanceAndNetAbstract" xlink:to="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" order="10720.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesLoansAndFinancingReceivableGrossAllowanceAndNetAbstract" xlink:to="us-gaap_LoansAndLeasesReceivableAllowance" order="10760.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesLoansAndFinancingReceivableGrossAllowanceAndNetAbstract" xlink:to="us-gaap_LoansAndLeasesReceivableNetReportedAmount" order="10800.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansDistributionOfFixedRateLoansAndVariableRateLoansByMajorLoanCategoryDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureLoansDistributionOfFixedRateLoansAndVariableRateLoansByMajorLoanCategoryDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansDistributionOfFixedRateLoansAndVariableRateLoansByMajorLoanCategoryDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansReceivableWithVariableRatesOfInterest1" xlink:type="locator" xlink:label="us-gaap_LoansReceivableWithVariableRatesOfInterest1" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansReceivableWithFixedRatesOfInterest1" xlink:type="locator" xlink:label="us-gaap_LoansReceivableWithFixedRatesOfInterest1" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_OtherLoanMember" xlink:type="locator" xlink:label="fmao_OtherLoanMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_ConsumerPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialRealEstatePortfolioSegmentMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgriculturalLoanMember" xlink:type="locator" xlink:label="fmao_AgriculturalLoanMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgricultureRealEstateMember" xlink:type="locator" xlink:label="fmao_AgricultureRealEstateMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ResidentialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_ResidentialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:type="locator" xlink:label="us-gaap_AccountsNotesAndLoansReceivableLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ResidentialPortfolioSegmentMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgricultureRealEstateMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgriculturalLoanMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialRealEstatePortfolioSegmentMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ConsumerPortfolioSegmentMember" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_OtherLoanMember" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_LoansReceivableWithFixedRatesOfInterest1" order="10240.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_LoansReceivableWithVariableRatesOfInterest1" order="10440.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansContractualAgingOfRecordedInvestmentInPastDueLoansByPortfolioClassificationOfLoansDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureLoansContractualAgingOfRecordedInvestmentInPastDueLoansByPortfolioClassificationOfLoansDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansContractualAgingOfRecordedInvestmentInPastDueLoansByPortfolioClassificationOfLoansDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="locator" xlink:label="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentCurrent" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentCurrent" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDue" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentPastDue" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivables60To89DaysPastDueMember" xlink:type="locator" xlink:label="us-gaap_FinancingReceivables60To89DaysPastDueMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivables30To59DaysPastDueMember" xlink:type="locator" xlink:label="us-gaap_FinancingReceivables30To59DaysPastDueMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_ConsumerPortfolioSegmentMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_CommercialAndIndustrialAndIndustrialDevelopmentBondsMember" xlink:type="locator" xlink:label="fmao_CommercialAndIndustrialAndIndustrialDevelopmentBondsMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialRealEstatePortfolioSegmentMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgriculturalLoanMember" xlink:type="locator" xlink:label="fmao_AgriculturalLoanMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgricultureRealEstateMember" xlink:type="locator" xlink:label="fmao_AgricultureRealEstateMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ResidentialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_ResidentialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:type="locator" xlink:label="us-gaap_AccountsNotesAndLoansReceivableLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" order="10030.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" order="10060.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ResidentialPortfolioSegmentMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgricultureRealEstateMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgriculturalLoanMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialRealEstatePortfolioSegmentMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_CommercialAndIndustrialAndIndustrialDevelopmentBondsMember" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ConsumerPortfolioSegmentMember" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_FinancingReceivablesPeriodPastDueAxis" order="10220.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:to="us-gaap_FinancingReceivablesPeriodPastDueDomain_2" order="10230.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:to="us-gaap_FinancingReceivablesPeriodPastDueDomain" order="10250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="us-gaap_FinancingReceivables30To59DaysPastDueMember" order="10270.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="us-gaap_FinancingReceivables60To89DaysPastDueMember" order="10290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember" order="10310.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentPastDue" order="10600.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentCurrent" order="11240.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" order="11400.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" order="11560.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansRecordedInvestmentInNonaccrualLoansByPortfolioClassOfLoansDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureLoansRecordedInvestmentInNonaccrualLoansByPortfolioClassOfLoansDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansRecordedInvestmentInNonaccrualLoansByPortfolioClassOfLoansDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_ConsumerPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialRealEstatePortfolioSegmentMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgriculturalLoanMember" xlink:type="locator" xlink:label="fmao_AgriculturalLoanMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgricultureRealEstateMember" xlink:type="locator" xlink:label="fmao_AgricultureRealEstateMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ResidentialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_ResidentialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:type="locator" xlink:label="us-gaap_AccountsNotesAndLoansReceivableLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ResidentialPortfolioSegmentMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgricultureRealEstateMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgriculturalLoanMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialRealEstatePortfolioSegmentMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ConsumerPortfolioSegmentMember" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus" order="10220.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansTierRiskRatingSystemAdditionalInformationDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureLoansTierRiskRatingSystemAdditionalInformationDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansTierRiskRatingSystemAdditionalInformationDetail">
    <link:loc xlink:href="fmao-20200930.xsd#fmao_RepaymentPeriodOfLoanWithReasonableReductionOfPrincipalBalance" xlink:type="locator" xlink:label="fmao_RepaymentPeriodOfLoanWithReasonableReductionOfPrincipalBalance" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_LeverageRatioTwo" xlink:type="locator" xlink:label="fmao_LeverageRatioTwo" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_SatisfactoryMember" xlink:type="locator" xlink:label="fmao_SatisfactoryMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MinimumMember" xlink:type="locator" xlink:label="srt_MinimumMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember" xlink:type="locator" xlink:label="srt_MaximumMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:type="locator" xlink:label="srt_RangeMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis" xlink:type="locator" xlink:label="srt_RangeAxis" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_GoodMember" xlink:type="locator" xlink:label="fmao_GoodMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InternalCreditAssessmentDomain" xlink:type="locator" xlink:label="us-gaap_InternalCreditAssessmentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InternalCreditAssessmentDomain" xlink:type="locator" xlink:label="us-gaap_InternalCreditAssessmentDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InternalCreditAssessmentAxis" xlink:type="locator" xlink:label="us-gaap_InternalCreditAssessmentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:type="locator" xlink:label="us-gaap_AccountsNotesAndLoansReceivableLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_InternalCreditAssessmentAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_InternalCreditAssessmentAxis" xlink:to="us-gaap_InternalCreditAssessmentDomain_2" order="10050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InternalCreditAssessmentAxis" xlink:to="us-gaap_InternalCreditAssessmentDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="fmao_GoodMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="srt_RangeAxis" order="10100.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="fmao_SatisfactoryMember" order="10230.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fmao_LeverageRatioTwo" order="10420.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fmao_RepaymentPeriodOfLoanWithReasonableReductionOfPrincipalBalance" order="10520.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansRiskCategoryOfLoansByPortfolioClassDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureLoansRiskCategoryOfLoansByPortfolioClassDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansRiskCategoryOfLoansByPortfolioClassDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="locator" xlink:label="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_OtherLoanMember" xlink:type="locator" xlink:label="fmao_OtherLoanMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialRealEstatePortfolioSegmentMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgriculturalLoanMember" xlink:type="locator" xlink:label="fmao_AgriculturalLoanMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgricultureRealEstateMember" xlink:type="locator" xlink:label="fmao_AgricultureRealEstateMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_LossMember" xlink:type="locator" xlink:label="fmao_LossMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DoubtfulMember" xlink:type="locator" xlink:label="us-gaap_DoubtfulMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubstandardMember" xlink:type="locator" xlink:label="us-gaap_SubstandardMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SpecialMentionMember" xlink:type="locator" xlink:label="us-gaap_SpecialMentionMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_SatisfactoryMonitoredMember" xlink:type="locator" xlink:label="fmao_SatisfactoryMonitoredMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_SatisfactoryMember" xlink:type="locator" xlink:label="fmao_SatisfactoryMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_ExcellentAndGoodMember" xlink:type="locator" xlink:label="fmao_ExcellentAndGoodMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InternalCreditAssessmentDomain" xlink:type="locator" xlink:label="us-gaap_InternalCreditAssessmentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InternalCreditAssessmentAxis" xlink:type="locator" xlink:label="us-gaap_InternalCreditAssessmentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:type="locator" xlink:label="us-gaap_AccountsNotesAndLoansReceivableLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_InternalCreditAssessmentAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InternalCreditAssessmentAxis" xlink:to="us-gaap_InternalCreditAssessmentDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="fmao_ExcellentAndGoodMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="fmao_SatisfactoryMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="fmao_SatisfactoryMonitoredMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="us-gaap_SpecialMentionMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="us-gaap_SubstandardMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="us-gaap_DoubtfulMember" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="fmao_LossMember" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" order="10220.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" order="10250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgricultureRealEstateMember" order="10270.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgriculturalLoanMember" order="10290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialRealEstatePortfolioSegmentMember" order="10310.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" order="10330.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_OtherLoanMember" order="10350.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" order="10700.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansRecordedInvestmentForConsumerLoansCreditQualityBasedOnStatusOfLoanAndPaymentActivityDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureLoansRecordedInvestmentForConsumerLoansCreditQualityBasedOnStatusOfLoanAndPaymentActivityDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansRecordedInvestmentForConsumerLoansCreditQualityBasedOnStatusOfLoanAndPaymentActivityDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NotesReceivableNet" xlink:type="locator" xlink:label="us-gaap_NotesReceivableNet" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="locator" xlink:label="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NonperformingFinancingReceivableMember" xlink:type="locator" xlink:label="us-gaap_NonperformingFinancingReceivableMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PerformingFinancingReceivableMember" xlink:type="locator" xlink:label="us-gaap_PerformingFinancingReceivableMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentPerformanceStatusDomain" xlink:type="locator" xlink:label="us-gaap_FinancialInstrumentPerformanceStatusDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentPerformanceStatusDomain" xlink:type="locator" xlink:label="us-gaap_FinancialInstrumentPerformanceStatusDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentPerformanceStatusAxis" xlink:type="locator" xlink:label="us-gaap_FinancialInstrumentPerformanceStatusAxis" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_ConsumerOtherFinancingReceivablesMember" xlink:type="locator" xlink:label="fmao_ConsumerOtherFinancingReceivablesMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditCardReceivablesMember" xlink:type="locator" xlink:label="us-gaap_CreditCardReceivablesMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ResidentialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_ResidentialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DoubtfulMember" xlink:type="locator" xlink:label="us-gaap_DoubtfulMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubstandardMember" xlink:type="locator" xlink:label="us-gaap_SubstandardMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SpecialMentionMember" xlink:type="locator" xlink:label="us-gaap_SpecialMentionMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PassMember" xlink:type="locator" xlink:label="us-gaap_PassMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InternalCreditAssessmentDomain" xlink:type="locator" xlink:label="us-gaap_InternalCreditAssessmentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InternalCreditAssessmentAxis" xlink:type="locator" xlink:label="us-gaap_InternalCreditAssessmentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:type="locator" xlink:label="us-gaap_AccountsNotesAndLoansReceivableLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_InternalCreditAssessmentAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InternalCreditAssessmentAxis" xlink:to="us-gaap_InternalCreditAssessmentDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="us-gaap_PassMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="us-gaap_SpecialMentionMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="us-gaap_SubstandardMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="us-gaap_DoubtfulMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" order="10160.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ResidentialPortfolioSegmentMember" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" order="10240.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2" order="10250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" order="10270.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_CreditCardReceivablesMember" order="10290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="fmao_ConsumerOtherFinancingReceivablesMember" order="10330.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_FinancialInstrumentPerformanceStatusAxis" order="10360.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentPerformanceStatusAxis" xlink:to="us-gaap_FinancialInstrumentPerformanceStatusDomain_2" order="10370.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentPerformanceStatusAxis" xlink:to="us-gaap_FinancialInstrumentPerformanceStatusDomain" order="10390.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancialInstrumentPerformanceStatusDomain" xlink:to="us-gaap_PerformingFinancingReceivableMember" order="10410.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancialInstrumentPerformanceStatusDomain" xlink:to="us-gaap_NonperformingFinancingReceivableMember" order="10430.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" order="10460.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_NotesReceivableNet" order="10690.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansImpairedLoansAdditionalInformationDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureLoansImpairedLoansAdditionalInformationDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansImpairedLoansAdditionalInformationDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MortgageLoansInProcessOfForeclosureAmount" xlink:type="locator" xlink:label="us-gaap_MortgageLoansInProcessOfForeclosureAmount" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RealEstateAcquiredThroughForeclosure" xlink:type="locator" xlink:label="us-gaap_RealEstateAcquiredThroughForeclosure" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_DelinquentPeriodForChargingDownCommercialAndAgriculturalCredits" xlink:type="locator" xlink:label="fmao_DelinquentPeriodForChargingDownCommercialAndAgriculturalCredits" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_DelinquentPeriodForChargingDownConsumerLoans" xlink:type="locator" xlink:label="fmao_DelinquentPeriodForChargingDownConsumerLoans" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_UnsecuredConsumerLoansCreditCardCreditsAndOverdraft" xlink:type="locator" xlink:label="fmao_UnsecuredConsumerLoansCreditCardCreditsAndOverdraft" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_ReEvaluationPeriodForRealEstate" xlink:type="locator" xlink:label="fmao_ReEvaluationPeriodForRealEstate" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_MaximumTimeForReevaluation" xlink:type="locator" xlink:label="fmao_MaximumTimeForReevaluation" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_FinancingReceivablesImpairedNumberOfTroubledDebtRestructuringWriteDown" xlink:type="locator" xlink:label="fmao_FinancingReceivablesImpairedNumberOfTroubledDebtRestructuringWriteDown" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentMaturityDate" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentMaturityDate" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableModificationsNumberOfContracts2" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableModificationsNumberOfContracts2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableModificationsRecordedInvestment" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableModificationsRecordedInvestment" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AdditionalFundsAvailableToBeAdvancedInConnectionWithImpairedLoans" xlink:type="locator" xlink:label="fmao_AdditionalFundsAvailableToBeAdvancedInConnectionWithImpairedLoans" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ResidentialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_ResidentialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialRealEstatePortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_RateConcessionAlongWithAmortizationExtendedMember" xlink:type="locator" xlink:label="fmao_RateConcessionAlongWithAmortizationExtendedMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_PaymentChangesFromMonthlyPaymentToPrincipalAndInterestAtMaturityMember" xlink:type="locator" xlink:label="fmao_PaymentChangesFromMonthlyPaymentToPrincipalAndInterestAtMaturityMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PrincipalForgivenessMember" xlink:type="locator" xlink:label="us-gaap_PrincipalForgivenessMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoanRestructuringModificationDomain" xlink:type="locator" xlink:label="us-gaap_LoanRestructuringModificationDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoanRestructuringModificationDomain" xlink:type="locator" xlink:label="us-gaap_LoanRestructuringModificationDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoanRestructuringModificationAxis" xlink:type="locator" xlink:label="us-gaap_LoanRestructuringModificationAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:type="locator" xlink:label="us-gaap_AccountsNotesAndLoansReceivableLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_LoanRestructuringModificationAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_LoanRestructuringModificationAxis" xlink:to="us-gaap_LoanRestructuringModificationDomain_2" order="10050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_LoanRestructuringModificationAxis" xlink:to="us-gaap_LoanRestructuringModificationDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LoanRestructuringModificationDomain" xlink:to="us-gaap_PrincipalForgivenessMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LoanRestructuringModificationDomain" xlink:to="fmao_PaymentChangesFromMonthlyPaymentToPrincipalAndInterestAtMaturityMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LoanRestructuringModificationDomain" xlink:to="fmao_RateConcessionAlongWithAmortizationExtendedMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" order="10160.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialRealEstatePortfolioSegmentMember" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ResidentialPortfolioSegmentMember" order="10290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fmao_AdditionalFundsAvailableToBeAdvancedInConnectionWithImpairedLoans" order="10340.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_FinancingReceivableModificationsRecordedInvestment" order="10390.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_FinancingReceivableModificationsNumberOfContracts2" order="10480.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_DebtInstrumentMaturityDate" order="10660.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fmao_FinancingReceivablesImpairedNumberOfTroubledDebtRestructuringWriteDown" order="10780.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1" order="10930.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fmao_MaximumTimeForReevaluation" order="11280.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fmao_ReEvaluationPeriodForRealEstate" order="11300.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fmao_UnsecuredConsumerLoansCreditCardCreditsAndOverdraft" order="11350.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fmao_DelinquentPeriodForChargingDownConsumerLoans" order="11370.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fmao_DelinquentPeriodForChargingDownCommercialAndAgriculturalCredits" order="11390.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_RealEstateAcquiredThroughForeclosure" order="11440.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_MortgageLoansInProcessOfForeclosureAmount" order="11480.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansImpairedLoansClassifiedAsTroubledDebtRestructuredDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureLoansImpairedLoansClassifiedAsTroubledDebtRestructuredDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansImpairedLoansClassifiedAsTroubledDebtRestructuredDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableModificationsNumberOfContracts2" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableModificationsNumberOfContracts2" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgriculturalLoanMember" xlink:type="locator" xlink:label="fmao_AgriculturalLoanMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialPortfolioSegmentMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgricultureRealEstateMember" xlink:type="locator" xlink:label="fmao_AgricultureRealEstateMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialRealEstatePortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ResidentialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_ResidentialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableModificationsLineItems" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableModificationsLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FinancingReceivableModificationsLineItems" xlink:to="us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ResidentialPortfolioSegmentMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialRealEstatePortfolioSegmentMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgricultureRealEstateMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgriculturalLoanMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableModificationsLineItems" xlink:to="us-gaap_FinancingReceivableModificationsNumberOfContracts2" order="10340.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableModificationsLineItems" xlink:to="us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2" order="10540.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableModificationsLineItems" xlink:to="us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2" order="10740.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansLoansIndividuallyEvaluatedForImpairmentByPortfolioClassOfLoansDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureLoansLoansIndividuallyEvaluatedForImpairmentByPortfolioClassOfLoansDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansLoansIndividuallyEvaluatedForImpairmentByPortfolioClassOfLoansDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableRecordedInvestment" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableRecordedInvestment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeAccrualMethod" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeAccrualMethod" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableRelatedAllowance" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableRelatedAllowance" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeAccrualMethod" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeAccrualMethod" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_ConsumerPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialRealEstatePortfolioSegmentMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgriculturalLoanMember" xlink:type="locator" xlink:label="fmao_AgriculturalLoanMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgricultureRealEstateMember" xlink:type="locator" xlink:label="fmao_AgricultureRealEstateMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ResidentialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_ResidentialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfImpairedFinancingReceivableTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfImpairedFinancingReceivableTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableImpairedLineItems" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableImpairedLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ScheduleOfImpairedFinancingReceivableTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfImpairedFinancingReceivableTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ResidentialPortfolioSegmentMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgricultureRealEstateMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgriculturalLoanMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialRealEstatePortfolioSegmentMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ConsumerPortfolioSegmentMember" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment" order="12460.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance" order="13000.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment" order="13540.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeAccrualMethod" order="14080.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod" order="14620.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment" order="15190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance" order="15730.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableRelatedAllowance" order="16270.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment" order="16810.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeAccrualMethod" order="17350.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod" order="17890.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableRecordedInvestment" order="18460.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance" order="19000.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment" order="20080.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod" order="20620.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod" order="21160.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansALLLAdditionalInformationDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureLoansALLLAdditionalInformationDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansALLLAdditionalInformationDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAccretableYield" xlink:type="locator" xlink:label="us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAccretableYield" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_BankOfGenevaMember" xlink:type="locator" xlink:label="fmao_BankOfGenevaMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:type="locator" xlink:label="us-gaap_BusinessAcquisitionAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:type="locator" xlink:label="us-gaap_AccountsNotesAndLoansReceivableLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_BusinessAcquisitionAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="fmao_BankOfGenevaMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAccretableYield" order="10120.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansAnalysisOfAllowanceForCreditLossesDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureLoansAnalysisOfAllowanceForCreditLossesDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureLoansAnalysisOfAllowanceForCreditLossesDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NotesReceivableNet" xlink:type="locator" xlink:label="us-gaap_NotesReceivableNet" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" xlink:type="locator" xlink:label="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_FinancingReceivablesAbstract" xlink:type="locator" xlink:label="fmao_FinancingReceivablesAbstract" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQualityEndingPeriod" xlink:type="locator" xlink:label="fmao_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQualityEndingPeriod" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_OtherNonInterestIncomeExpenseRecoveryRelatedToUnfunded" xlink:type="locator" xlink:label="fmao_OtherNonInterestIncomeExpenseRecoveryRelatedToUnfunded" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProvisionForLoanAndLeaseLosses" xlink:type="locator" xlink:label="us-gaap_ProvisionForLoanAndLeaseLosses" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts" xlink:type="locator" xlink:label="us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs" xlink:type="locator" xlink:label="us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLosses" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AllowanceForCreditLossesAbstract" xlink:type="locator" xlink:label="fmao_AllowanceForCreditLossesAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UnallocatedFinancingReceivablesMember" xlink:type="locator" xlink:label="us-gaap_UnallocatedFinancingReceivablesMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_ConsumerPortfolioSegmentMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_CommercialAndIndustrialAndIndustrialDevelopmentBondsMember" xlink:type="locator" xlink:label="fmao_CommercialAndIndustrialAndIndustrialDevelopmentBondsMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialRealEstatePortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialRealEstatePortfolioSegmentMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgriculturalLoanMember" xlink:type="locator" xlink:label="fmao_AgriculturalLoanMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_AgricultureRealEstateMember" xlink:type="locator" xlink:label="fmao_AgricultureRealEstateMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ResidentialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_ResidentialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_UnfundedLoanCommitmentAndLettersOfCreditMember" xlink:type="locator" xlink:label="fmao_UnfundedLoanCommitmentAndLettersOfCreditMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" order="10040.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" order="10100.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="fmao_UnfundedLoanCommitmentAndLettersOfCreditMember" order="10120.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" order="10160.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ResidentialPortfolioSegmentMember" order="10180.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgricultureRealEstateMember" order="10200.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_AgriculturalLoanMember" order="10220.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialRealEstatePortfolioSegmentMember" order="10240.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fmao_CommercialAndIndustrialAndIndustrialDevelopmentBondsMember" order="10260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ConsumerPortfolioSegmentMember" order="10280.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_UnallocatedFinancingReceivablesMember" order="10300.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="fmao_AllowanceForCreditLossesAbstract" order="11290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_AllowanceForCreditLossesAbstract" xlink:to="us-gaap_FinancingReceivableAllowanceForCreditLosses" order="11690.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_AllowanceForCreditLossesAbstract" xlink:to="us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs" order="11890.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_AllowanceForCreditLossesAbstract" xlink:to="us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts" order="12090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_AllowanceForCreditLossesAbstract" xlink:to="us-gaap_ProvisionForLoanAndLeaseLosses" order="12290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_AllowanceForCreditLossesAbstract" xlink:to="fmao_OtherNonInterestIncomeExpenseRecoveryRelatedToUnfunded" order="12490.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_AllowanceForCreditLossesAbstract" xlink:to="us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1" order="12890.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_AllowanceForCreditLossesAbstract" xlink:to="us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment" order="13090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_AllowanceForCreditLossesAbstract" xlink:to="fmao_FinancingReceivableAllowanceForCreditLossesAcquiredWithDeterioratedCreditQualityEndingPeriod" order="13290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="fmao_FinancingReceivablesAbstract" order="13490.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_FinancingReceivablesAbstract" xlink:to="us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome" order="13890.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_FinancingReceivablesAbstract" xlink:to="us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment" order="14090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_FinancingReceivablesAbstract" xlink:to="us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment" order="14290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_FinancingReceivablesAbstract" xlink:to="us-gaap_NotesReceivableNet" order="14490.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsAdditionalInformationDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureFairValueOfFinancialInstrumentsAdditionalInformationDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsAdditionalInformationDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableRelatedAllowance" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableRelatedAllowance" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableRecordedInvestment" xlink:type="locator" xlink:label="us-gaap_ImpairedFinancingReceivableRecordedInvestment" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_MaximumMaturityPeriodOfCarryingAmountInterestBearingDeposits" xlink:type="locator" xlink:label="fmao_MaximumMaturityPeriodOfCarryingAmountInterestBearingDeposits" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CollateralPledgedMember" xlink:type="locator" xlink:label="us-gaap_CollateralPledgedMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CollateralDomain" xlink:type="locator" xlink:label="us-gaap_CollateralDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CollateralDomain" xlink:type="locator" xlink:label="us-gaap_CollateralDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CollateralAxis" xlink:type="locator" xlink:label="us-gaap_CollateralAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:type="locator" xlink:label="us-gaap_FairValueInputsLevel3Member" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2" order="10050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_CollateralAxis" order="10120.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_CollateralAxis" xlink:to="us-gaap_CollateralDomain_2" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_CollateralAxis" xlink:to="us-gaap_CollateralDomain" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CollateralDomain" xlink:to="us-gaap_CollateralPledgedMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="fmao_MaximumMaturityPeriodOfCarryingAmountInterestBearingDeposits" order="10220.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableRecordedInvestment" order="10270.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_ImpairedFinancingReceivableRelatedAllowance" order="10350.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsEstimatedFairValuesAndRelatedCarryingOrNotionalAmountsDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureFairValueOfFinancialInstrumentsEstimatedFairValuesAndRelatedCarryingOrNotionalAmountsDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsEstimatedFairValuesAndRelatedCarryingOrNotionalAmountsDetail">
    <link:loc xlink:href="fmao-20200930.xsd#fmao_InterestPayableFairValueDisclosure" xlink:type="locator" xlink:label="fmao_InterestPayableFairValueDisclosure" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FederalHomeLoanBankBorrowingsFairValueDisclosure" xlink:type="locator" xlink:label="us-gaap_FederalHomeLoanBankBorrowingsFairValueDisclosure" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FederalFundsPurchasedAndSecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure" xlink:type="locator" xlink:label="us-gaap_FederalFundsPurchasedAndSecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DepositsFairValueDisclosure" xlink:type="locator" xlink:label="us-gaap_DepositsFairValueDisclosure" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:type="locator" xlink:label="us-gaap_LiabilitiesFairValueDisclosureAbstract" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_InterestReceivableFairValueDisclosure" xlink:type="locator" xlink:label="fmao_InterestReceivableFairValueDisclosure" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansReceivableFairValueDisclosure" xlink:type="locator" xlink:label="us-gaap_LoansReceivableFairValueDisclosure" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansHeldForSaleFairValueDisclosure" xlink:type="locator" xlink:label="us-gaap_LoansHeldForSaleFairValueDisclosure" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SecuritiesBorrowedFairValueDisclosure" xlink:type="locator" xlink:label="us-gaap_SecuritiesBorrowedFairValueDisclosure" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_InterestBearingTimeDepositsFairValueDisclosure" xlink:type="locator" xlink:label="fmao_InterestBearingTimeDepositsFairValueDisclosure" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_CashCashEquivalentsAndFederalFundsSoldFairValueDisclosure" xlink:type="locator" xlink:label="fmao_CashCashEquivalentsAndFederalFundsSoldFairValueDisclosure" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsFairValueDisclosureAbstract" xlink:type="locator" xlink:label="us-gaap_AssetsFairValueDisclosureAbstract" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:type="locator" xlink:label="us-gaap_EstimateOfFairValueFairValueDisclosureMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:type="locator" xlink:label="us-gaap_CarryingReportedAmountFairValueDisclosureMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain" xlink:type="locator" xlink:label="us-gaap_FairValueDisclosureItemAmountsDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:type="locator" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByMeasurementBasisAxis" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_TimeDepositsMember" xlink:type="locator" xlink:label="fmao_TimeDepositsMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_NonInterestBearingDepositsMember" xlink:type="locator" xlink:label="fmao_NonInterestBearingDepositsMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_InterestBearingDepositsLiabilityMember" xlink:type="locator" xlink:label="fmao_InterestBearingDepositsLiabilityMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:type="locator" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:type="locator" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByLiabilityClassAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByLiabilityClassAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:type="locator" xlink:label="us-gaap_FairValueInputsLevel3Member" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:type="locator" xlink:label="us-gaap_FairValueInputsLevel2Member" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:type="locator" xlink:label="us-gaap_FairValueInputsLevel1Member" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="us-gaap_FairValueByLiabilityClassAxis" order="10140.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByLiabilityClassAxis" xlink:to="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByLiabilityClassAxis" xlink:to="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:to="fmao_InterestBearingDepositsLiabilityMember" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:to="fmao_NonInterestBearingDepositsMember" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:to="fmao_TimeDepositsMember" order="10230.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="us-gaap_FairValueByMeasurementBasisAxis" order="10240.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByMeasurementBasisAxis" xlink:to="us-gaap_PortionAtFairValueFairValueDisclosureMember" order="10250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueDisclosureItemAmountsDomain" xlink:to="us-gaap_PortionAtFairValueFairValueDisclosureMember" order="10260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByMeasurementBasisAxis" xlink:to="us-gaap_FairValueDisclosureItemAmountsDomain" order="10290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueDisclosureItemAmountsDomain" xlink:to="us-gaap_CarryingReportedAmountFairValueDisclosureMember" order="10310.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueDisclosureItemAmountsDomain" xlink:to="us-gaap_EstimateOfFairValueFairValueDisclosureMember" order="10330.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="us-gaap_AssetsFairValueDisclosureAbstract" order="10660.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsFairValueDisclosureAbstract" xlink:to="fmao_CashCashEquivalentsAndFederalFundsSoldFairValueDisclosure" order="10860.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsFairValueDisclosureAbstract" xlink:to="fmao_InterestBearingTimeDepositsFairValueDisclosure" order="10960.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsFairValueDisclosureAbstract" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecurities" order="11060.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsFairValueDisclosureAbstract" xlink:to="us-gaap_SecuritiesBorrowedFairValueDisclosure" order="11160.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsFairValueDisclosureAbstract" xlink:to="us-gaap_LoansHeldForSaleFairValueDisclosure" order="11260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsFairValueDisclosureAbstract" xlink:to="us-gaap_LoansReceivableFairValueDisclosure" order="11360.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsFairValueDisclosureAbstract" xlink:to="fmao_InterestReceivableFairValueDisclosure" order="11460.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="us-gaap_LiabilitiesFairValueDisclosureAbstract" order="11560.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:to="us-gaap_DepositsFairValueDisclosure" order="11760.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:to="us-gaap_FederalFundsPurchasedAndSecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure" order="12160.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:to="us-gaap_FederalHomeLoanBankBorrowingsFairValueDisclosure" order="12260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:to="fmao_InterestPayableFairValueDisclosure" order="12360.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureFairValueOfFinancialInstrumentsFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementsRecurringMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:type="locator" xlink:label="us-gaap_FairValueInputsLevel3Member" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:type="locator" xlink:label="us-gaap_FairValueInputsLevel2Member" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:type="locator" xlink:label="us-gaap_FairValueInputsLevel1Member" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember" xlink:type="locator" xlink:label="us-gaap_USStatesAndPoliticalSubdivisionsMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:type="locator" xlink:label="us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:type="locator" xlink:label="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_USTreasurySecuritiesMember" xlink:type="locator" xlink:label="us-gaap_USTreasurySecuritiesMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:type="locator" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="us-gaap_FinancialInstrumentAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USTreasurySecuritiesMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USStatesAndPoliticalSubdivisionsMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" order="10160.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" order="10230.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" order="10250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" order="10260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain_2" order="10270.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" order="10290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsRecurringMember" order="10310.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecurities" order="10780.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsChangesInLevel3FairValueCategoryOfUnobservableInputsDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureFairValueOfFinancialInstrumentsChangesInLevel3FairValueCategoryOfUnobservableInputsDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsChangesInLevel3FairValueCategoryOfUnobservableInputsDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchasesSalesIssuancesSettlements" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchasesSalesIssuancesSettlements" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember" xlink:type="locator" xlink:label="us-gaap_USStatesAndPoliticalSubdivisionsMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_USStatesAndPoliticalSubdivisionsTaxableDebtSecuritiesMember" xlink:type="locator" xlink:label="fmao_USStatesAndPoliticalSubdivisionsTaxableDebtSecuritiesMember" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_USStatesAndPoliticalSubdivisionsTaxExemptDebtSecuritiesMember" xlink:type="locator" xlink:label="fmao_USStatesAndPoliticalSubdivisionsTaxExemptDebtSecuritiesMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:type="locator" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="us-gaap_FinancialInstrumentAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="fmao_USStatesAndPoliticalSubdivisionsTaxExemptDebtSecuritiesMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="fmao_USStatesAndPoliticalSubdivisionsTaxableDebtSecuritiesMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USStatesAndPoliticalSubdivisionsMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue" order="10460.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1" order="10540.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchasesSalesIssuancesSettlements" order="10620.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsQuantitativeInformationAboutUnobservableInputsUsedInRecurringAndNonrecurringLevel3FairValueMeasurementsDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureFairValueOfFinancialInstrumentsQuantitativeInformationAboutUnobservableInputsUsedInRecurringAndNonrecurringLevel3FairValueMeasurementsDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsQuantitativeInformationAboutUnobservableInputsUsedInRecurringAndNonrecurringLevel3FairValueMeasurementsDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherRealEstateOwnedMeasurementInputExtensibleList" xlink:type="locator" xlink:label="us-gaap_OtherRealEstateOwnedMeasurementInputExtensibleList" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherRealEstateOwnedValuationTechniqueExtensibleList" xlink:type="locator" xlink:label="us-gaap_OtherRealEstateOwnedValuationTechniqueExtensibleList" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherRealEstate" xlink:type="locator" xlink:label="us-gaap_OtherRealEstate" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherRealEstateOwnedMeasurementInput" xlink:type="locator" xlink:label="us-gaap_OtherRealEstateOwnedMeasurementInput" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ServicingAssetMeasurementInputExtensibleList" xlink:type="locator" xlink:label="us-gaap_ServicingAssetMeasurementInputExtensibleList" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ServicingAssetValuationTechniqueExtensibleList" xlink:type="locator" xlink:label="us-gaap_ServicingAssetValuationTechniqueExtensibleList" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ServicingAsset" xlink:type="locator" xlink:label="us-gaap_ServicingAsset" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput" xlink:type="locator" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleMeasurementInputExtensibleList" xlink:type="locator" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleMeasurementInputExtensibleList" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleValuationTechniqueExtensibleList" xlink:type="locator" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleValuationTechniqueExtensibleList" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_ImpairedLoansMember" xlink:type="locator" xlink:label="fmao_ImpairedLoansMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember" xlink:type="locator" xlink:label="us-gaap_USStatesAndPoliticalSubdivisionsMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:type="locator" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_WeightedAverageMember" xlink:type="locator" xlink:label="srt_WeightedAverageMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember" xlink:type="locator" xlink:label="srt_MaximumMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MinimumMember" xlink:type="locator" xlink:label="srt_MinimumMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:type="locator" xlink:label="srt_RangeMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis" xlink:type="locator" xlink:label="srt_RangeAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:type="locator" xlink:label="us-gaap_FairValueInputsLevel3Member" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="srt_RangeAxis" order="10100.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_WeightedAverageMember" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" order="10200.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" order="10230.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" order="10250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FinancialInstrumentAxis" order="10260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="10290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USStatesAndPoliticalSubdivisionsMember" order="10310.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="fmao_ImpairedLoansMember" order="10330.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecurities" order="11860.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleValuationTechniqueExtensibleList" order="11920.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleMeasurementInputExtensibleList" order="11980.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput" order="12040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_ServicingAsset" order="12250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_ServicingAssetValuationTechniqueExtensibleList" order="12310.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_ServicingAssetMeasurementInputExtensibleList" order="12370.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_OtherRealEstateOwnedMeasurementInput" order="12430.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_OtherRealEstate" order="12640.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_OtherRealEstateOwnedValuationTechniqueExtensibleList" order="12700.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_OtherRealEstateOwnedMeasurementInputExtensibleList" order="12760.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsImpairedLoansAndOtherRealEstateDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureFairValueOfFinancialInstrumentsImpairedLoansAndOtherRealEstateDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsImpairedLoansAndOtherRealEstateDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherRealEstate" xlink:type="locator" xlink:label="us-gaap_OtherRealEstate" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ServicingAsset" xlink:type="locator" xlink:label="us-gaap_ServicingAsset" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_ImpairedLoansMember" xlink:type="locator" xlink:label="fmao_ImpairedLoansMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:type="locator" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:type="locator" xlink:label="us-gaap_FairValueInputsLevel3Member" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:type="locator" xlink:label="us-gaap_FairValueInputsLevel2Member" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:type="locator" xlink:label="us-gaap_FairValueInputsLevel1Member" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:type="locator" xlink:label="us-gaap_CommercialPortfolioSegmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:type="locator" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsNonrecurringMember" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementsNonrecurringMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsNonrecurringMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" order="10120.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" order="10180.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" order="10230.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" order="10250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" order="10270.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FinancialInstrumentAxis" order="10280.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="10310.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="fmao_ImpairedLoansMember" order="10330.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_ServicingAsset" order="11260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_OtherRealEstate" order="11690.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchaseScheduleOfRemainingContractualMaturityInRepurchaseAgreementsDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchaseScheduleOfRemainingContractualMaturityInRepurchaseAgreementsDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchaseScheduleOfRemainingContractualMaturityInRepurchaseAgreementsDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase" xlink:type="locator" xlink:label="us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SecuritiesSoldUnderAgreementsToRepurchase" xlink:type="locator" xlink:label="us-gaap_SecuritiesSoldUnderAgreementsToRepurchase" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FederalFundsPurchased" xlink:type="locator" xlink:label="us-gaap_FederalFundsPurchased" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MaturityOver90DaysMember" xlink:type="locator" xlink:label="us-gaap_MaturityOver90DaysMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Maturity30To90DaysMember" xlink:type="locator" xlink:label="us-gaap_Maturity30To90DaysMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MaturityUpTo30DaysMember" xlink:type="locator" xlink:label="us-gaap_MaturityUpTo30DaysMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MaturityOvernightMember" xlink:type="locator" xlink:label="us-gaap_MaturityOvernightMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain" xlink:type="locator" xlink:label="us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain" xlink:type="locator" xlink:label="us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis" xlink:type="locator" xlink:label="us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_USTreasuryAndGovernmentMember" xlink:type="locator" xlink:label="us-gaap_USTreasuryAndGovernmentMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:type="locator" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAssetsSoldUnderAgreementsToRepurchaseTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAssetsSoldUnderAgreementsToRepurchaseTable" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseLineItems" xlink:type="locator" xlink:label="us-gaap_AssetsSoldUnderAgreementsToRepurchaseLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_AssetsSoldUnderAgreementsToRepurchaseLineItems" xlink:to="us-gaap_ScheduleOfAssetsSoldUnderAgreementsToRepurchaseTable" order="10030.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAssetsSoldUnderAgreementsToRepurchaseTable" xlink:to="us-gaap_FinancialInstrumentAxis" order="10060.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USTreasuryAndGovernmentMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAssetsSoldUnderAgreementsToRepurchaseTable" xlink:to="us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis" order="10120.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis" xlink:to="us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_2" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis" xlink:to="us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain" xlink:to="us-gaap_MaturityOvernightMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain" xlink:to="us-gaap_MaturityUpTo30DaysMember" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain" xlink:to="us-gaap_Maturity30To90DaysMember" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain" xlink:to="us-gaap_MaturityOver90DaysMember" order="10230.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsSoldUnderAgreementsToRepurchaseLineItems" xlink:to="us-gaap_FederalFundsPurchased" order="10440.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsSoldUnderAgreementsToRepurchaseLineItems" xlink:to="us-gaap_SecuritiesSoldUnderAgreementsToRepurchase" order="10540.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AssetsSoldUnderAgreementsToRepurchaseLineItems" xlink:to="us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase" order="10640.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fm.bank/20200930/taxonomy/role/DisclosureRecentAccountingPronouncementsAdditionalInformationDetail" xlink:href="fmao-20200930.xsd#Role_DisclosureRecentAccountingPronouncementsAdditionalInformationDetail" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fm.bank/20200930/taxonomy/role/DisclosureRecentAccountingPronouncementsAdditionalInformationDetail">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1" xlink:type="locator" xlink:label="us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateImmaterialEffect" xlink:type="locator" xlink:label="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateImmaterialEffect" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateAdoptionDate" xlink:type="locator" xlink:label="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateAdoptionDate" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateAdopted" xlink:type="locator" xlink:label="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateAdopted" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountingStandardsUpdate201813Member" xlink:type="locator" xlink:label="us-gaap_AccountingStandardsUpdate201813Member" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountingStandardsUpdate201704Member" xlink:type="locator" xlink:label="us-gaap_AccountingStandardsUpdate201704Member" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:type="locator" xlink:label="us-gaap_TypeOfAdoptionMember" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:type="locator" xlink:label="us-gaap_TypeOfAdoptionMember_2" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:type="locator" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_SummaryOfSignificantAccountingPoliciesTable" xlink:type="locator" xlink:label="fmao_SummaryOfSignificantAccountingPoliciesTable" />
    <link:loc xlink:href="fmao-20200930.xsd#fmao_SummaryOfSignificantAccountingPoliciesLineItems" xlink:type="locator" xlink:label="fmao_SummaryOfSignificantAccountingPoliciesLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="fmao_SummaryOfSignificantAccountingPoliciesLineItems" xlink:to="fmao_SummaryOfSignificantAccountingPoliciesTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="fmao_SummaryOfSignificantAccountingPoliciesTable" xlink:to="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="us-gaap_TypeOfAdoptionMember_2" order="10050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="us-gaap_TypeOfAdoptionMember" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TypeOfAdoptionMember" xlink:to="us-gaap_AccountingStandardsUpdate201704Member" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TypeOfAdoptionMember" xlink:to="us-gaap_AccountingStandardsUpdate201813Member" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_SummaryOfSignificantAccountingPoliciesLineItems" xlink:to="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateAdopted" order="10140.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_SummaryOfSignificantAccountingPoliciesLineItems" xlink:to="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateAdoptionDate" order="10180.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_SummaryOfSignificantAccountingPoliciesLineItems" xlink:to="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateImmaterialEffect" order="10220.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="fmao_SummaryOfSignificantAccountingPoliciesLineItems" xlink:to="us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1" order="10290.00" priority="2" use="optional" />
  </link:definitionLink>
</link:linkbase>
