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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Changes in the Allowance for Loan Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Allowance for Credit Loss [Table Text Block]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FraudActivityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Fraud activity.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FraudActivityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fraud activity [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FraudActivityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fraud Activity [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PlanNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Plan Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PlanNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Plan Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivables60To89DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">60 to 89 Days Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivables60To89DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Asset, 60 to 89 Days Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativesFairValueLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivatives, Fair Value [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativesFairValueLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivatives, Fair Value [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetAccumulatedAmortization_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Accumulated amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetAccumulatedAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Right Of Use Asset Accumulated Amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetAccumulatedAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating lease right of use asset accumulated amortization.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressPostalZipCode_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, Postal Zip Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressPostalZipCode_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, Postal Zip Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Federal Home Loan Bank ("FHLB") and Federal Reserve Bank ("FRB") stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">FHLB and FRB stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Federal Home Loan Bank Stock and Federal Reserve Bank Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Federal Home Loan Bank Stock and Federal Reserve Bank Stock, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Disposal Group Name [Axis]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherRealEstateOwnedOtherReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Other real estate owned other receivable.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableforsaleSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Available for Sale Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableforsaleSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Available-for-Sale Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other comprehensive income (loss), before Reclassifications, Tax Effect</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss) before Reclassifications, Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other Comprehensive Income (Loss) before Reclassifications, Tax, Total</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amounts Reclassified Out of Each Component of Accumulated Other Comprehensive (Loss) Income</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Recurring and Nonrecurring [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_BasisOfPresentationAndSignificantAccountingPoliciesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Basis of presentation and significant accounting policies</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityIncorporationStateCountryCode_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Incorporation, State or Country Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityIncorporationStateCountryCode_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Incorporation, State or Country Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestructuringCharges_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restructuring recoveries</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestructuringCharges_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Restructuring Charges, Total</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestructuringCharges_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Restructuring (recoveries) charges</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestPaidNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash paid for interest</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfInterestRateDerivativesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Company's Outstanding Interest Rate Swaps</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BusinessCombinationDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Business Combinations</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BusinessCombinationDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Business Combination Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, Year Four</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2028</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromLifeInsurancePolicies_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds received from surrender of company owned life insurance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromLifeInsurancePolicies_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Life Insurance Policy</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">U.S. Government Agency And Government Sponsored Enterprises [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">US Government-sponsored Enterprises Debt Securities [Member]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IntangibleAssetsNetIncludingGoodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Intangible Assets, Net (Including Goodwill), Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel2Member_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Level 2 Inputs [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel2Member_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Inputs, Level 2 [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-based Compensation Arrangement by Share-based Payment Award [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases term description</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Description</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueDisclosureItemAmountsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Measurement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueDisclosureItemAmountsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfStockByClassTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Changes in Shares of Common Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfStockByClassTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Stock by Class [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DepositRelatedChargedOffItems_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Deposit related charged-off items.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DepositRelatedChargedOffItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deposit Related Charged-off Items</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DepositRelatedChargedOffItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deposit-related charged-off items</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoninterestIncomeLoanServicing_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loan servicing</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoninterestIncomeLoanServicing_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Noninterest Income Loan Servicing</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoninterestIncomeLoanServicing_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Noninterest income loan servicing.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassification out of Accumulated Other Comprehensive Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification out of Accumulated Other Comprehensive Income [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeasesTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Leases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeasesTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Leases [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due in one year or less, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, Year One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments and Contingencies</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitments and Contingencies Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liability derivatives</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Liability, Subject to Master Netting Arrangement, before Offset</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Derivative Liability, Fair Value, Gross Liability, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Derivative instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestRateSwapMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest Rate Swap [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestRateSwapMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Rate Swap [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted stock awards issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherAssetsAndOtherLiabilitiesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">The entire disclosure for other assets and other liabilities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherAssetsAndOtherLiabilitiesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets and Other Liabilities Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherAssetsAndOtherLiabilitiesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Assets and Other Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets by Major Class [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-based compensation plans:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Noncash Expense [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfLeaseCostsAndOtherLeaseInformationTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Lease Costs and Other Lease Information</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfLeaseCostsAndOtherLeaseInformationTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Lease Costs And Other Lease Information Table [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfLeaseCostsAndOtherLeaseInformationTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of lease costs and other lease information.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of RSAs granted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BankOwnedLifeInsuranceIncome_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Income on company owned life insurance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BankOwnedLifeInsuranceIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Company owned life insurance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BankOwnedLifeInsuranceIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Bank Owned Life Insurance Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockRepurchasedDuringPeriodShares_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Repurchased During Period, Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockRepurchasedDuringPeriodShares_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of shares repurchased</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableCreditQualityIndicatorsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commercial Loan Portfolio Categorized by Internally Assigned Asset Classification</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableCreditQualityIndicatorsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable Credit Quality Indicators [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cumulative Effect, Period of Adoption</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cumulative Effect, Period of Adoption [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shareholders' Equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_TitleOfIndividualAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Title of Individual</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_TitleOfIndividualAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Title and Position [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoansOnBusinessAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collateral dependent loans on business assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoansOnBusinessAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateral Dependent Loans On Business Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoansOnBusinessAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateral dependent loans on business assets.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Inputs, Assets, Quantitative Information [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement Inputs and Valuation Techniques [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCentralIndexKey_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Central Index Key</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCentralIndexKey_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Central Index Key</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other comprehensive (loss) income, Pre-tax Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrivateEquityFundsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Privately issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrivateEquityFundsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Private Equity Funds [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnfundedLoanCommitmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unfunded Commitments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnfundedLoanCommitmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Unfunded Loan Commitment [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_GainOnDivestitureOfInterestInConsolidatedSubsidiaries_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Gain on divestiture of interest in consolidated subsidiaries</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_GainOnDivestitureOfInterestInConsolidatedSubsidiaries_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Gain on Divestiture of Interest in Consolidated Subsidiaries</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_GainOnDivestitureOfInterestInConsolidatedSubsidiaries_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gain on divestiture of interest in consolidated subsidiaries</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_StockReleasedDuringPeriodSharesRestrictedStockAwards_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Stock released during period shares restricted stock awards.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_StockReleasedDuringPeriodSharesRestrictedStockAwards_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Released During Period Shares Restricted Stock Awards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_StockReleasedDuringPeriodSharesRestrictedStockAwards_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted stock awards released</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionTwoMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Interest rate swap transaction two.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionTwoMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Rate Swap Transaction Two [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionTwoMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest Rate Swap Transaction Two [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ValuationTechniqueDiscountedCashFlowMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Discounted Cash Flow [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ValuationTechniqueDiscountedCashFlowMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Valuation Technique, Discounted Cash Flow [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_USStatesAndPoliticalSubdivisionsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">State And Political Subdivisions [Member]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Shares issued, beginning balance</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Shares, Issued</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InternalCreditAssessmentAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Internal Credit Assessment</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total other assets</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CreditRiskContractMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Credit Contract [Member]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherIntangibleAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Intangible Assets [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherIntangibleAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Intangible Assets [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BankOwnedLifeInsurance_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Bank Owned Life Insurance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BankOwnedLifeInsurance_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Company owned life insurance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement Inputs and Valuation Techniques [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ConsumerOverdraftsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Consumer Overdrafts [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ConsumerOverdraftsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Consumer Overdrafts [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ConsumerOverdraftsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Consumer Overdrafts [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PastDueFinancingReceivablesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recorded Investment by Loan Class in Current and Nonaccrual Loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PastDueFinancingReceivablesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Past Due [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities held to maturity, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Securities held to maturity, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred Equity [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Statement [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressStateOrProvince_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, State or Province</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressStateOrProvince_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, State or Province</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Income (loss) before income taxes</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_UnrealizedLossOnInvestmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investments Gross Unrealized Losses and Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_UnrealizedLossOnInvestmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Unrealized Loss on Investments [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_UnrealizedLossOnInvestmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Tabular disclosure of unrealized loss on investments.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnDerivativeInstrumentsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income from Derivative Instruments, Net [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnDerivativeInstrumentsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Gain (Loss) on Derivative Instruments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_COVIDNineteenMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">COVID-19 [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_COVIDNineteenMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">C O V I D Nineteen [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_COVIDNineteenMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">COVID 19.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnrealizedGainLossOnInvestmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amortized Cost and Fair Value of Investment Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnrealizedGainLossOnInvestmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Unrealized Gain (Loss) on Investments [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Amortization of unrecognized net actuarial loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Benefit Plan, Amortization of Gain (Loss)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Disclosure Item Amounts [Default]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Portion at Fair Value Measurement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember_lbl" xlink:role="http://fasb.org/us-gaap/role/label/axisDefault">Portion at Fair Value Measurement [Member] [Default]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShortTermBorrowings_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Short-term borrowings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShortTermBorrowings_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Short-Term Debt</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShortTermBorrowings_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Short-term Debt, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassification out of Accumulated Other Comprehensive (Loss) Income [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification out of Accumulated Other Comprehensive Income [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfInvestmentsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Investments [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfInvestmentsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Investments [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ResidentialRealEstateMortgagesServicedForOthers_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Residential real estate mortgages serviced for others</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ResidentialRealEstateMortgagesServicedForOthers_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Residential Real Estate Mortgages Serviced For Others</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ResidentialRealEstateMortgagesServicedForOthers_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Residential Real Estate Mortgages Serviced For Others</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Securities available for sale, Fair Value, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Unrealized Loss Position</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoansOnRealProperty_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collateral dependent loans on real property</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoansOnRealProperty_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateral Dependent Loans On Real Property</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoansOnRealProperty_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateral dependent loans on real property.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, Year Three</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2027</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeaseCostAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lease, Cost [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeaseCostAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease costs:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByLiabilityClassAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liability Class</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByLiabilityClassAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liability Class [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfImpairedFinancingReceivableTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Impaired Financing Receivable [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfImpairedFinancingReceivableTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Impaired Financing Receivable [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsClassifiedByContractualMaturityDateTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Scheduled Maturities of Securities Available for Sale and Securities Held to Maturity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsClassifiedByContractualMaturityDateTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investments Classified by Contractual Maturity Date [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommercialRealEstateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commercial Mortgage [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommercialRealEstateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commercial Real Estate [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonShares_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Common, Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonShares_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Treasury stock, beginning balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonShares_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Treasury stock, ending balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonShares_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Treasury stock, shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndDividendIncomeOperatingAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest income:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndDividendIncomeOperatingAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest and Dividend Income, Operating [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CoverAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cover [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoansHeldForSaleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loans Held For Sale [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoansHeldForSaleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loans Held For Sale [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoansHeldForSaleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Loans held for sale.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SpecialMentionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Special Mention [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SpecialMentionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Special Mention [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Basic earnings per common share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share, Basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Earnings Per Share, Basic, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassification out of Accumulated Other Comprehensive Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification out of Accumulated Other Comprehensive Income [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CreditLossBenefitExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Credit Loss Benefit Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CreditLossBenefitExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Credit loss benefit expense.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CreditLossBenefitExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Credit (benefit) loss for unfunded commitments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale, Unrealized Gains</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Securities available for sale, Unrealized Gains</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageBackedSecuritiesFederalHomeLoanMortgageCorporationCertificatesAndObligationsFhlmcMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateralized Mortgage-Backed Securities Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC).</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageBackedSecuritiesFederalHomeLoanMortgageCorporationCertificatesAndObligationsFhlmcMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage-Backed Securities Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesAcquisitions_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares issued for Landmark Group acquisition</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesAcquisitions_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period, Shares, Acquisitions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedGainLossCashFlowHedgeIncludingNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedGainLossCashFlowHedgeIncludingNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total other liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ConsolidationItemsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Consolidation Items</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ConsolidationItemsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Consolidation Items [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Instruments and Hedging Activities Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Instrument and Hedging Activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableNonaccrualNoAllowance_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Nonaccrual with no allowance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableNonaccrualNoAllowance_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Nonaccrual, No Allowance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investment securities, nonaccrual</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Nonaccrual</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsFederalNationalMortgageAssociationCertificatesAndObligationsFnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateralized Mortgage Obligations Federal National Mortgage Association Certificates and Obligations (FNMA).</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsFederalNationalMortgageAssociationCertificatesAndObligationsFnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage Obligations Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Long-term borrowings, net of issuance costs of $313 and $468, respectively</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Long-Term Debt</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Long-term Debt, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Long-term borrowings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DirectorStockIncentivePlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-employee Directors Stock Incentive Plan [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DirectorStockIncentivePlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Director Stock Incentive Plan [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DirectorStockIncentivePlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Director stock incentive plan.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Retained earnings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Retained Earnings (Accumulated Deficit)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Retained Earnings (Accumulated Deficit), Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Retained Earnings (Accumulated Deficit), Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Retained Earnings (Accumulated Deficit), Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsNonrecurringMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Measured On A Nonrecurring Basis [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsNonrecurringMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Nonrecurring [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PlanNameAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Plan Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PlanNameAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Plan Name [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForProceedsFromLifeInsurancePolicies_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net proceeds from (payments for) company owned life insurance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForProceedsFromLifeInsurancePolicies_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments for (Proceeds from) Life Insurance Policies</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForProceedsFromLifeInsurancePolicies_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Payments for (Proceeds from) Life Insurance Policies, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_USTreasuryBillSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">US Treasury Bill Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_USTreasuryBillSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">U.S. Treasury Bills [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoncashRestructuringChargesAgainstAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-cash restructuring recoveries against assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoncashRestructuringChargesAgainstAssets_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Charges against assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoncashRestructuringChargesAgainstAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Noncash Restructuring Charges Against Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoncashRestructuringChargesAgainstAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Noncash restructuring charges against assets.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtAndEquitySecuritiesGainLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net loss on investment securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtAndEquitySecuritiesGainLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt and Equity Securities, Gain (Loss)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtAndEquitySecuritiesGainLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Debt and Equity Securities, Gain (Loss), Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtAndEquitySecuritiesGainLoss_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net (loss) gain on investment securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtAndEquitySecuritiesGainLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Net (loss) gain on investment securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFour_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Rolling Year Four</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFour_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2027</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investment Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Type [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash provided by operating activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided by (Used in) Operating Activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassification, Pre-tax Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Reclassification, Pre-tax Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total reclassified for the period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel">Reclassification before tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepositsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deposits:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepositsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deposits [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Other Comprehensive Income (Loss), Net of Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Accumulated Other Comprehensive Income (Loss), Net of Tax, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated other comprehensive loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prior Fiscal Year 1</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SalariesAndEmployeeBenefitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Salaries and Employee Benefits [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SalariesAndEmployeeBenefitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Salaries And Employee Benefits [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SalariesAndEmployeeBenefitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Salaries and Employee Benefits [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Premises and equipment, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Property, Plant and Equipment, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Property, Plant and Equipment, Net, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Property, Plant and Equipment, Net, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Property, Plant and Equipment, Net, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from operating activities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided by (Used in) Operating Activities [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NatureOfBusinessOperationsPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Nature of Operations</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NatureOfBusinessOperationsPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Nature Of Business Operations Policy [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NatureOfBusinessOperationsPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Nature Of Business Operations [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsToExtendCreditMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments To Extend Credit [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsToExtendCreditMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitments to Extend Credit [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsRecurringMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Measured On A Recurring Basis [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsRecurringMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Recurring [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NondesignatedMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivatives Not Designated as Hedging Instruments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NondesignatedMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Not Designated as Hedging Instrument [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, par value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Par or Stated Value Per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesAccumulatedUnrecognizedHoldingLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities Accumulated Unrecognized Holding Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesAccumulatedUnrecognizedHoldingLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount of accumulated pre-tax unrealized loss on securities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesAccumulatedUnrecognizedHoldingLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total AFS debt securities with unrealized losses, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Measurement Input Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input Type [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComprehensiveIncomeNetOfTaxAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Comprehensive income (loss):</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComprehensiveIncomeNetOfTaxAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementOfCashFlowsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Cash Flows [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentFinancingReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collateral Dependent Loans [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentFinancingReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateral Dependent Financing Receivable [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentFinancingReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateral dependent financing receivable.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseShortTermBorrowings_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Short-term borrowings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseShortTermBorrowings_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Expense, Short-Term Borrowings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseShortTermBorrowings_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Interest Expense, Short-term Borrowings, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Antidilutive Securities, Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities, Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LongTermDebtFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Long-term borrowings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LongTermDebtFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Long-Term Debt, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Asset, Period Past Due</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Asset, Aging [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ShareholdersEquityLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shareholders Equity [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ShareholdersEquityLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Shareholders Equity [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ShareholdersEquityLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Shareholders Equity [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amortization of unrecognized prior service credit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Benefit Plan, Amortization of Prior Service Cost (Credit)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsNotesAndLoansReceivableLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts, Notes, Loans and Financing Receivable [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsNotesAndLoansReceivableLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounts, Notes, Loans and Financing Receivable [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromDivestitureOfInterestInConsolidatedSubsidiaries_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Divestiture of Interest in Consolidated Subsidiaries</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromDivestitureOfInterestInConsolidatedSubsidiaries_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from divestiture of interest in consolidated subsidiaries</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeGainLossOnDerivativeNet_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Gain (loss) recognized in income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeGainLossOnDerivativeNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative, Gain (Loss) on Derivative, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeGainLossOnDerivativeNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Derivative, Gain (Loss) on Derivative, Net, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeGainLossOnDerivativeNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income from derivative instruments, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted Stock Awards [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restricted Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">RSAs [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementEquityComponentsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Equity Components</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementEquityComponentsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity Components [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Allowance for credit losses - loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Loans, allowance for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Allowance for credit loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Beginning balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Ending balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Allowance for Credit Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressAddressLine1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, Address Line One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressAddressLine1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, Address Line One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SuppliesAndPostageExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Supplies and postage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SuppliesAndPostageExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Supplies and Postage Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SuppliesAndPostageExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Supplies and Postage Expense, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reconciliation of Earnings and Shares Used in Calculating Basic and Diluted EPS</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForOriginationAndPurchasesOfLoansHeldForSale_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Originations of loans held for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForOriginationAndPurchasesOfLoansHeldForSale_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payment for Origination and Purchase, Loan, Held-for-Sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForOriginationAndPurchasesOfLoansHeldForSale_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Payments for Origination and Purchases of Loans Held-for-sale, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Granted, Number of Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Restricted shares of common stock awarded</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Intangible Asset, Finite-Lived [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HedgingDesignationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Hedging Designation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HedgingDesignationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Hedging Designation [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ValuationTechniqueAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Valuation Approach and Technique</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ValuationTechniqueAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Valuation Approach and Technique [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares Excluded from Computation of Diluted EPS</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireHeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments to Acquire Held-to-Maturity Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireHeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of held to maturity securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Hedging Relationship</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Hedging Relationship [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsPayableFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued interest payable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsPayableFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounts Payable, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net (decrease) increase in deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Increase (Decrease) in Deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Increase (Decrease) in Deposits, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnamortizedDebtIssuanceExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt issuance costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnamortizedDebtIssuanceExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Unamortized Debt Issuance Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investment Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, Year Two</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2026</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_AmendmentFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Amendment Flag</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_AmendmentFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Amendment Flag</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoanRestructuringModificationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loan Restructuring Modification</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoanRestructuringModificationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loan Restructuring Modification [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Values Derivatives Balance Sheet Location By Derivative Contract Type By Hedging Designation [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestRateContractMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Interest Rate Products [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestRateContractMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest Rate Swaps [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestRateContractMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Rate Contract [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SeriesB1EightPointFourEightPercentagePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series B-1 8.48% Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SeriesB1EightPointFourEightPercentagePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Series B1 Eight Point Four Eight Percentage Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SeriesB1EightPointFourEightPercentagePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Series B-1 Eight Point four eight percentage preferred stock.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Business Segment Profit (Loss)</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndDividendIncomeOperating_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total interest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndDividendIncomeOperating_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest and Dividend Income, Operating</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net periodic benefit expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Benefit Plan, Net Periodic Benefit Cost (Credit)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock options exercised</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CashFlowReportingPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash Flow Reporting</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CashFlowReportingPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Flow Reporting Policy [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CashFlowReportingPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Cash flow reporting.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_VestedImmediatelyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Vested Immediately [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_VestedImmediatelyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Vested Immediately [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_VestedImmediatelyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Vested immediately.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EquityComponentDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity Component [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RangeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statistical Measurement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RangeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statistical Measurement [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Government National Mortgage Association [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Government National Mortgage Association Certificates and Obligations (GNMA) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prior Fiscal Year 2</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PerformingFinancingReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Performing [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PerformingFinancingReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Performing Financial Instruments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Charge-offs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Allowance for Credit Loss, Writeoff</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Financing Receivable, Allowance for Credit Loss, Writeoff, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndDueFromBanks_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash and due from banks</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndDueFromBanks_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash and Due from Banks</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndDueFromBanks_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Cash and Due from Banks, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansAndLeasesReceivableAllowance_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Allowance for credit losses - loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansAndLeasesReceivableAllowance_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loans, allowance for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansAndLeasesReceivableAllowance_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loans and Leases Receivable, Allowance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansAndLeasesReceivableAllowance_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Loans and Leases Receivable, Allowance, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansAndLeasesReceivableAllowance_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Loans and Leases Receivable, Allowance, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansAndLeasesReceivableAllowance_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Loans and Leases Receivable, Allowance, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Common [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Treasury Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesIssuedBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total shares issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesIssuedBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number of Shares Issued, Basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Defined Benefit Plans Adjustment, Net Prior Service Including Portion Attributable to Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Defined Benefit Plans Adjustment, Net Prior Service Including Portion Attributable to Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProfitLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProfitLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Net Income (Loss), Including Portion Attributable to Noncontrolling Interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProfitLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, shares issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Shares Issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Preferred Stock, Shares Issued, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeasePayments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating cash flows from operating leases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeasePayments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Payments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Asset derivatives</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Asset, Subject to Master Netting Arrangement, before Offset</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Derivative Asset, Fair Value, Gross Asset, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfOtherAssetsAndOtherLiabilitiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Other Assets and Other Liabilities [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfOtherAssetsAndOtherLiabilitiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Other Assets and Other Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InternalCreditAssessmentDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Internal Credit Assessment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InternalCreditAssessmentDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Internal Credit Assessment [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Securities held to maturity, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities held to maturity, fair value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Employee Benefit Plans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Retirement Benefits [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionsTwelveMonthsOrLongerQualitativeDisclosureNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of security positions, unrealized loss position for more than 12 months</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionsTwelveMonthsOrLongerQualitativeDisclosureNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities In Unrealized Loss Positions Twelve Months Or Longer Qualitative Disclosure Number Of Positions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionsTwelveMonthsOrLongerQualitativeDisclosureNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Disclosure regarding factors used to determine that the impairment of securities not categorized as either held-to-maturity securities or trading securities (hence equal to available for sale securities) where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the available-for-sale investments determined to be temporarily impaired for twelve months or longer.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Financing Receivable Recorded Investment Credit Quality Indicator [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Credit Quality Indicator [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due after five years through ten years, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year 5 through 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturityRestricted_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities pledged as collateral</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturityRestricted_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities Available For Sale And Held To Maturity Restricted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturityRestricted_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Debt securities available for sale and held to maturity restricted.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ReturnOnAverageAssetsPerformanceRequirementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">ROAA Performance Requirement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ReturnOnAverageAssetsPerformanceRequirementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Return On Average Assets Performance Requirement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ReturnOnAverageAssetsPerformanceRequirementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Return on average assets performance requirement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFinancingReceivablesPastDueTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Financing Receivables Past Due [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFinancingReceivablesPastDueTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Past Due [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ConsolidationItemsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Consolidation Items</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ConsolidationItemsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Consolidation Items [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalHomeLoanBankCertificatesAndObligationsFHLBMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Federal Home Loan Bank Certificates and Obligations (FHLB) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalHomeLoanBankCertificatesAndObligationsFHLBMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">FHLB [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionBenefitForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Benefit Provision for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionBenefitForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Provision (benefit) for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionBenefitForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Provision Benefit For Credit Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionBenefitForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Provision (Benefit) for credit losses.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionBenefitForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Provision for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfStockDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfStockDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Stock [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SubordinatedNotesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Subordinated notes</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SubordinatedNotesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subordinated Notes [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SubordinatedNotesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subordinated notes [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total other comprehensive income (loss), net of tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss), Net of Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other comprehensive income (loss), net of tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Net current period other comprehensive income (loss)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllowanceForNotesAndLoansReceivableCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Allowance for Credit Loss, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cumulative-Effect Adjustment [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cumulative Effect, Period of Adoption, Adjustment [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross Carrying Amount Accumulated Amortization and Net Book Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Finite-Lived Intangible Assets [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Comprehensive income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Comprehensive Income (Loss), Net of Tax, Attributable to Parent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Shares outstanding, beginning balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Shares outstanding, ending balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Shares, Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Provision for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Provision for credit losses - loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Provision For Credit Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Provision for credit losses.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">(Benefit) provision for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets, Major Class Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, off-Balance-Sheet Risks, Disclosure Information [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeExpenseNet_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Net interest income (expense)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeExpenseNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net interest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeExpenseNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeExpenseNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Income (Expense), Operating</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivables30To89DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Financing Receivables 30 To 89 Days Past Due</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivables30To89DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivables 30 To 89 Days Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivables30To89DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">30-89 Days Past Due</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of available for sale securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments to Acquire Debt Securities, Available-for-Sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, par value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Par or Stated Value Per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from principal payments, maturities and calls on available for sale securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-Sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherLiabilitiesMiscellaneous_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Other liabilities miscellaneous.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherLiabilitiesMiscellaneous_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Liabilities Miscellaneous</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherLiabilitiesMiscellaneous_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MortgagesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Mortgage Banking [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MortgagesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Mortgages [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_WeightedAverageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Weighted Average [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_WeightedAverageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FraudulentActivityPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Fraudulent Activity Policy.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FraudulentActivityPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fraudulent Activity Policy [ Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FraudulentActivityPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fraudulent Activity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MunicipalBondsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Municipal Bonds [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MunicipalBondsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Municipal Bonds [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Antidilutive Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loans held for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Held-for-Sale, Not Part of Disposal Group, after Valuation Allowance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Financing Receivable, Held-for-Sale, Not Part of Disposal Group, after Valuation Allowance, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Financing Receivable, Held-for-Sale, Not Part of Disposal Group, after Valuation Allowance, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansHeldForSaleFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loans held for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansHeldForSaleFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loan, Held-for-Sale, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityInteractiveDataCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Interactive Data Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityInteractiveDataCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Interactive Data Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due in one year or less, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommitmentsAndContingenciesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments And Contingencies [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommitmentsAndContingenciesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitments And Contingencies [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommitmentsAndContingenciesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Commitments and contingencies.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldtomaturitySecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Held To Maturity Investment Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldtomaturitySecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Held To Maturity Investment Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldtomaturitySecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Held-to-Maturity Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NumberOfNonEmployeeDirectors_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of non-employee directors</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NumberOfNonEmployeeDirectors_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Non Employee Directors</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NumberOfNonEmployeeDirectors_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of non employee directors.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringAndNonrecurringBasisTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Assets Measured at Fair Value on a Recurring and Non-Recurring Basis</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringAndNonrecurringBasisTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepositsSavingsDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Savings and money market</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepositsSavingsDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deposits, Savings Deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSaleOfBusiness_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel">Net gain on sale of assets of subsidiary</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSaleOfBusiness_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Gain (Loss) on Disposition of Business</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Liabilities [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Liabilities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherDebtSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other debt securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherDebtSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Debt Obligations [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TypeOfAdoptionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounting Standards Update</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TypeOfAdoptionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounting Standards Update [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentQuarterlyReport_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Quarterly Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentQuarterlyReport_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Quarterly Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BalanceSheetLocationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Balance Sheet Location</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BalanceSheetLocationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Financial Position Location, Balance [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RangeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statistical Measurement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RangeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statistical Measurement [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, Year Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2029</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Assets at fair value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Assets at fair value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Assets, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Assets, Fair Value Disclosure, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_PaycheckProtectionProgramMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Paycheck Protection Program [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_PaycheckProtectionProgramMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Paycheck Protection Program [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_PaycheckProtectionProgramMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Paycheck protection program.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net lease costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lease, Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Instruments, Liabilities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Financial Instruments, Liabilities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NonMaturityDepositsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-maturity deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NonMaturityDepositsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Non Maturity Deposits Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NonMaturityDepositsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Non-Maturity Deposits Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageBackedSecuritiesFederalNationalMortgageAssociationCertificatesAndObligationsFnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateralized Mortgage-Backed Securities Federal National Mortgage Association Certificates and Obligations (FNMA).</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageBackedSecuritiesFederalNationalMortgageAssociationCertificatesAndObligationsFnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage-Backed Securities Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Future Minimum Payments Under Non cancellable Operating Leases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_DirectorMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Director [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_DirectorMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Director [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Assets measured at fair value on recurring basis using significant unobservable inputs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross carrying amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets, Gross</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Finite-Lived Intangible Assets, Gross, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestPayableCurrentAndNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Payable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestPayableCurrentAndNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued interest expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net interest income after provision (benefit) for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Income (Expense), after Provision for Loan Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basis of Presentation and Summary of Significant Accounting Policies</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Basis of Presentation and Significant Accounting Policies [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoans_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Collateral dependent loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoans_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateral Dependent Loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoans_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateral dependent loans.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ManagementStockIncentivePlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Management Stock Incentive Plan [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ManagementStockIncentivePlanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Management Stock Incentive Plan [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Grant date fair value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Granted, Weighted Average Market Price at Grant Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Expected recognition expense period, weighted average period in years</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShorttermDebtFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Short-term borrowings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShorttermDebtFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Short-Term Debt, Fair Value</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndOtherIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest and Other Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndOtherIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Interest and Other Income, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TransferToOtherRealEstate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Real estate and other assets acquired in settlement of loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TransferToOtherRealEstate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Real Estate Owned, Transfer to Real Estate Owned</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsLiabilitiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Deferred Tax Assets, Net, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsLiabilitiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsLiabilitiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net deferred tax asset</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByMeasurementBasisAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated Fair Value [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByMeasurementBasisAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Basis [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Statement Location</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Income Location, Balance [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRevolvingConvertedToTermLoan_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revolving Loans Converted to Term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRevolvingConvertedToTermLoan_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Revolving, Converted to Term Loan</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetGainLossIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetGainLossIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Assets_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Assets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Assets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TimeDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Time deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TimeDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Time Deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TimeDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Time Deposits, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InternallyRatedHeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Internally rated held-to-maturity securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InternallyRatedHeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Internally Rated Held To Maturity Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InternallyRatedHeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Internally rated held-to-maturity securities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Long-Term Debt Instruments [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ReturnOnAverageEquityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">ROAE Return on Average Equity [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ReturnOnAverageEquityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Return On Average Equity [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ReturnOnAverageEquityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Return on average equity.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnusualOrInfrequentItemDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unusual or Infrequent Item, or Both</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnusualOrInfrequentItemDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Unusual or Infrequent Item, or Both [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedNetInvestmentGainLossIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities Available for Sale and Transferred Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedNetInvestmentGainLossIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-Sale, Including Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DividendsPayableCurrentAndNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued and declared unpaid dividends</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DividendsPayableCurrentAndNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Dividends Payable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoanWithSpecificReserve_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collateral dependent loan with specific reserve</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoanWithSpecificReserve_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateral Dependent Loan With Specific Reserve</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoanWithSpecificReserve_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateral dependent loan with specific reserve.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recent Accounting Pronouncements</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressCityOrTown_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, City or Town</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressCityOrTown_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, City or Town</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Accumulated Other Comprehensive Income (Loss) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">AOCI Attributable to Parent [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Other Comprehensive Loss [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net Actuarial Losses [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementBusinessSegmentsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">All Other [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementBusinessSegmentsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segments [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfNetBenefitCostsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Components of Net Periodic Benefit Expense</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalDepositInsuranceCorporationPremiumExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">FDIC assessments</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OccupancyNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Occupancy and equipment</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionThreeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Interest rate swap transaction three.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionThreeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest Rate Swap Transaction Three [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CurrentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Current.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CurrentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Current [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CurrentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ConsumerPortfolioSegmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Consumer [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ConsumerPortfolioSegmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Consumer Portfolio Segment [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HedgingRelationshipDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Hedging Relationship</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Pension and post-retirement obligations</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfProductiveAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from sale of assets of subsidiary</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Segment Reporting Information By Segment [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Segment Reporting Information, by Segment [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due in one year or less, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-Based Compensation Plans</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MortgageBankingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Mortgage Banking [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MortgageBankingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Mortgage Banking [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash paid for amounts included in the measurement of lease liabilities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Paid For Amounts Included In Measurement Of Lease Liabilities [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Cash paid for amounts included in measurement of lease liabilities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_PaymentsForProceedsFromLifeInsurancePolicies1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments For Proceeds From Life Insurance Policies 1</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_PaymentsForProceedsFromLifeInsurancePolicies1_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">The net cash outflow or inflow for net proceeds and payments derived from carrying life insurance policies for which the entity is the beneficiary.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_PaymentsForProceedsFromLifeInsurancePolicies1_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net payments for company owned life insurance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsGovernmentNationalMortgageAssociationCertificatesAndObligationsGnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateralized mortgage obligations government national mortgage association certificates and obligations Gnma.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsGovernmentNationalMortgageAssociationCertificatesAndObligationsGnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage Obligations Government National Mortgage Association Certificates And Obligations Gnma [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities held to maturity, Unrealized Gains</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Accumulated Unrecognized Gain</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases, weighted-average discount rate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Weighted Average Discount Rate, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Other Comprehensive Income (Loss) [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Other Comprehensive Income (Loss) [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Assets [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueDisclosuresAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Disclosures [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_GainLossOnDispositionOfOtherAssets_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel">Net gain on other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_GainLossOnDispositionOfOtherAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Gain Loss on Disposition of Other Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_GainLossOnDispositionOfOtherAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Gain loss on disposition of other assets.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recoveries</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Allowance for Credit Loss, Recovery</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated reclassification to interest expense during next twelve months</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsMortgageBackedSecuritiesIssuedByPrivateEnterprisesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateralized Mortgage Obligations Mortgage-Backed Securities, Issued by Private Enterprises.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsMortgageBackedSecuritiesIssuedByPrivateEnterprisesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage Obligations Mortgage-Backed Securities, Issued by Private Enterprises [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestBearingDepositLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest-bearing demand</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestBearingDepositLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest-Bearing Deposit Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestBearingDepositLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Interest-bearing Deposit Liabilities, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxesPaidNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash paid for income taxes</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxesPaidNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Taxes Paid, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxesPaidNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Income Taxes Paid, Net, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentType_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Document Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentType_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounting Standards Update</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounting Standards Update [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearThree_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Rolling Year Three</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearThree_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2026</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Adjusted Balance [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cumulative Effect, Period of Adoption, Adjusted Balance [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsFederalHomeLoanMortgageCorporationCertificatesAndObligationsFhlmcMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateralized Mortgage Obligations Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC).</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsFederalHomeLoanMortgageCorporationCertificatesAndObligationsFhlmcMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage Obligations Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProvisionForOtherCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Provision for Other Credit Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProvisionForOtherCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Provision for credit loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueLiabilitiesLevel2ToLevel1TransferAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Level 2 to Level 1 transfers, liabilities amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueLiabilitiesLevel2ToLevel1TransferAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Liabilities, Level 2 to Level 1 Transfer, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueLiabilitiesLevel2ToLevel1TransferAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount of transfers of liabilities measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_Security12bTitle_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Title of 12(b) Security</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_Security12bTitle_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Title of 12(b) Security</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investments Gross Unrealized Losses and Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Unrealized Loss on Investments [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BalanceSheetLocationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Balance Sheet Location</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BalanceSheetLocationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Financial Position Location, Balance [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_AllowanceForCreditLossesAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Allowance for credit losses, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_AllowanceForCreditLossesAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Allowance For Credit Losses Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_AllowanceForCreditLossesAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Allowance for credit losses, amortized cost.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementOfStockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Stockholders' Equity [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Fiscal Period Focus</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Fiscal Period Focus</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total noninterest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Noninterest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Noninterest Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Expense, Tax Benefit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income tax benefit realized for compensation costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfGoodwillTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Changes in Carrying Amount of Goodwill</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfGoodwillTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Goodwill [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CurrentPeriodGrossWriteOffsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Current Period Gross Write-offs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CurrentPeriodGrossWriteOffsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Current Period Gross Write-offs [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CurrentPeriodGrossWriteOffsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current Period Gross Write-offs [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostCreditExcludingServiceCostStatementOfIncomeOrComprehensiveIncomeExtensibleList_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsOfDividends_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Cash dividends paid to common and preferred shareholders</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsOfDividends_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments of Dividends</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsOfDividends_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Payments of Dividends, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MarketingAndAdvertisingExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Advertising and promotions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MarketingAndAdvertisingExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Marketing and Advertising Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MarketingAndAdvertisingExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Marketing and Advertising Expense, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockDividendRatePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, dividend percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockDividendRatePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Dividend Rate, Percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Asset Class</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Asset Class [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanInterestCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest cost on projected benefit obligation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanInterestCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Benefit Plan, Interest Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansNotesTradeAndOtherReceivablesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loans</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsGainLossLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Instruments, Gain (Loss) [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_VestedAfterCompletionOfOneYearServiceRequirementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Vested After Completion of One-Year Service Requirement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_VestedAfterCompletionOfOneYearServiceRequirementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Vested After Completion Of One Year Service Requirement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_VestedAfterCompletionOfOneYearServiceRequirementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Vested after completion of one year service requirement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EstimateOfFairValueFairValueDisclosureMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated Fair Value [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EstimateOfFairValueFairValueDisclosureMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Estimate of Fair Value Measurement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearTwo_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Rolling Year Two</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearTwo_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2025</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MortgageBackedSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Mortgage-Backed Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MortgageBackedSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage-Backed Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingSegmentsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating Segment [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingSegmentsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Segments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRevolving_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revolving Loans Amortized Cost Basis</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRevolving_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Revolving</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due after ten years, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TroubledDebtRestructuringsOnFinancingReceivablesPerformanceOfLoansTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Troubled debt restructurings on financing receivables performance of loans.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TroubledDebtRestructuringsOnFinancingReceivablesPerformanceOfLoansTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Troubled Debt Restructurings On Financing Receivables Performance of Loans [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TroubledDebtRestructuringsOnFinancingReceivablesPerformanceOfLoansTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Performance of Loans that are Modified to Borrowers Experiencing Financial Difficulty</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Fair Value Off Balance Sheet Risks [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, off-Balance-Sheet Risk [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale, 12 months or longer, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Instruments [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherNoninterestExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Noninterest Expense [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherNoninterestExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Noninterest Expenses [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherNoninterestExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Other noninterest expenses that are not performance, advisory, custodian, directors' fees, offering costs, commission expenses or printing and fulfillment costs and are not covered in any other noninterest expense category.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prior</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Originated, More than Five Years before Current Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Hedging Derivative Instruments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DividendsPreferredStockCash_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Preferred stock dividends per share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DividendsPreferredStockCash_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Dividends, Preferred Stock, Cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from investing activities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided by (Used in) Investing Activities [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeCategorizationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeCategorizationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investments [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForRepurchaseOfCommonStock_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of common stock for treasury</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForRepurchaseOfCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments for Repurchase of Common Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfCreditLossExpenseBenefitForUnfundedCommitmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of credit loss expense benefit for unfunded commitments.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfCreditLossExpenseBenefitForUnfundedCommitmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Credit Loss Expense Benefit for Unfunded Commitments [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfCreditLossExpenseBenefitForUnfundedCommitmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Credit Loss Expense Benefit for Unfunded Commitments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockDividendsPerShareDeclared_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Common stock dividends per share, declared</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockDividendsPerShareDeclared_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash dividends declared per common share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockDividendsPerShareDeclared_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Dividends, Per Share, Declared</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Comprehensive Income [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Other Comprehensive Income Loss [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Other Comprehensive Income (Loss) [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfLoansHeldForSale_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from sale of loans held for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfLoansHeldForSale_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Sale, Loan, Held-for-Sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfLoansHeldForSale_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Proceeds from Sale of Loans Held-for-sale, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DesignatedAsHedgingInstrumentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivatives Designated as Hedging Instruments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DesignatedAsHedgingInstrumentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Designated as Hedging Instrument [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanDisclosureLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Defined Contribution Plan Disclosure [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanDisclosureLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan Disclosure [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loans (net of allowance for credit losses of $43,952 and $51,082, respectively)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total loans, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financing receivables, amortized cost basis</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableNet_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Financing receivables, amortized cost basis</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResidentialMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Residential Real Estate Loans [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResidentialMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Residential Mortgage [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Other intangible assets, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Finite-Lived Intangible Assets, Net, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Finite-Lived Intangible Assets, Net, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperationalAccountingAndReportingImpactsRelatedToCovidPandemicPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operational, Accounting and Reporting Impacts Related to the COVID-19 Pandemic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperationalAccountingAndReportingImpactsRelatedToCovidPandemicPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operational Accounting And Reporting Impacts Related To Covid Pandemic Policy [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperationalAccountingAndReportingImpactsRelatedToCovidPandemicPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Operational accounting and reporting impacts related to Covid pandemic.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_PerformanceShareUnitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">PSUs [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_PerformanceShareUnitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Performance Share Units [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_PerformanceShareUnitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Performance Share Units [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepreciationAndAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Depreciation and amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepreciationAndAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Depreciation, Depletion and Amortization, Nonproduction</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepreciationAndAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Depreciation, Depletion and Amortization, Nonproduction, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ConsumerIndirectMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Consumer Indirect [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ConsumerIndirectMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Consumer Indirect [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ConsumerIndirectMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Consumer Indirect [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">LIABILITIES AND SHAREHOLDERS&#8217; EQUITY</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities and Equity [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentPeriodEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Period End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentPeriodEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Period End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due in one year or less, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, Year One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash (used in) provided by financing activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided by (Used in) Financing Activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Greater than 90 Days [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Asset, Equal to or Greater than 90 Days Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">90+ Days Past Due</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityNoteAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders' Equity Note [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfClassificationOfRightOfUseAssetsAndLeaseLiabilitiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Classification of Right of Use Assets and Lease Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfClassificationOfRightOfUseAssetsAndLeaseLiabilitiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Classification Of Right Of Use Assets And Lease Liabilities Table [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfClassificationOfRightOfUseAssetsAndLeaseLiabilitiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of classification of right of use assets and lease liabilities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted stock awards issued</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Antidilutive shares excluded from computation of diluted EPS</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CarryingReportedAmountFairValueDisclosureMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Carrying Amount [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CarryingReportedAmountFairValueDisclosureMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reported Value Measurement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due from one to five years, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-based compensation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">APIC, Share-Based Payment Arrangement, Increase for Cost Recognition</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">APIC, Share-based Payment Arrangement, Increase for Cost Recognition, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommitmentsAndContingenciesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments And Contingencies [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommitmentsAndContingenciesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitments And Contingencies [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommitmentsAndContingenciesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Commitments and contingencies.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel">Income tax (expense) benefit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income tax expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Expense (Benefit)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Income tax expense, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Income tax expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DividendsCommonStockCash_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Common stock dividends per share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DividendsCommonStockCash_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Dividends, Common Stock, Cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesRestrictedStock_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Unvested restricted stock awards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesRestrictedStock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number of Shares, Restricted Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LongLivedAssetsHeldForSaleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Long-lived Assets Held for Sale [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LongLivedAssetsHeldForSaleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Long Lived Assets Held For Sale [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LongLivedAssetsHeldForSaleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Long-lived assets held for sale.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Year One, Originated, Current Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities held to maturity, allowance for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Allowance for Credit Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Debt Securities, Held-to-maturity, Allowance for Credit Loss, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Debt Securities, Held-to-maturity, Allowance for Credit Loss, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Debt Securities, Held-to-maturity, Allowance for Credit Loss, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_TradingSymbol_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Trading Symbol</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_TradingSymbol_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Trading Symbol</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BusinessCombinationsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Business Combinations [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total shareholders&#8217; equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity, Attributable to Parent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loans [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loans [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Hedging derivative instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionsLessThanTwelveMonthsQualitativeDisclosureNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of security positions, unrealized loss position for less than 12 months</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionsLessThanTwelveMonthsQualitativeDisclosureNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities In Unrealized Loss Positions Less Than Twelve Months Qualitative Disclosure Number Of Positions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionsLessThanTwelveMonthsQualitativeDisclosureNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Disclosure regarding factors used to determine that the impairment of securities not categorized as either held-to-maturity securities or trading securities (hence equal to available for sale securities) where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the available-for-sale investments determined to be temporarily impaired for less than twelve months.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterRollingYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Thereafter</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterRollingYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, after Rolling Year Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Expected return on plan assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Benefit Plan, Expected Return (Loss) on Plan Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoninterestIncomeInvestmentsInLimitedPartnerships_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investments in limited partnerships</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoninterestIncomeInvestmentsInLimitedPartnerships_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Noninterest Income Investments In Limited Partnerships</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoninterestIncomeInvestmentsInLimitedPartnerships_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Noninterest income from investments in limited partnerships.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BrokerageCommissionsRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investment advisory</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BrokerageCommissionsRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Brokerage Commissions Revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueAssetsLevel1ToLevel2TransferAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Level 1 to Level 2 transfers, assets amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueAssetsLevel1ToLevel2TransferAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Assets, Level 1 to Level 2 Transfer, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueAssetsLevel1ToLevel2TransferAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueAssetsLevel2ToLevel1TransferAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Level 2 to Level 1 transfers, assets amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueAssetsLevel2ToLevel1TransferAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Assets, Level 2 to Level 1 Transfer, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueAssetsLevel2ToLevel1TransferAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivableAllowanceForLoanLossesProvisionCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Provision (benefit)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivableAllowanceForLoanLossesProvisionCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable Allowance For Loan Losses Provision Credit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivableAllowanceForLoanLossesProvisionCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Financing receivable allowance for loan losses, provision (credit).</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentRiskAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Instrument</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentRiskAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Instrument [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">This item represents the fair value of securities that have been in a continuous unrealized loss position for twelve months or longer.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities, 12 months or longer, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total AFS debt securities with unrealized losses, 12 months or longer, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedStockUnitsRSUMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">RSUs [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedStockUnitsRSUMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restricted Stock Units (RSUs) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CoreDepositsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Core Deposits [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CoreDepositsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Core Deposits [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_VariableLeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Variable lease costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_VariableLeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Variable Lease, Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForProceedsFromLoansAndLeases_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net loan originations</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForProceedsFromLoansAndLeases_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments for (Proceeds from) Loans and Leases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForProceedsFromLoansAndLeases_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Payments for (Proceeds from) Loans and Leases, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Carrying amount of goodwill</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Goodwill, beginning balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Goodwill, ending balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Goodwill, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFinancialInstrumentsAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Instruments, Assets [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFinancialInstrumentsAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Financial Instruments, Assets [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unrecognized compensation expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DividendsCashAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash dividends declared:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DividendsCashAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Dividends, Cash [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-Based Compensation Expense and The Total Income Tax Benefit Included In Consolidated Statements of Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Employer contribution</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan, Employer Discretionary Contribution Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputDiscountRateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Discount Rate [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputDiscountRateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input, Discount Rate [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loan Portfolio</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Defined Benefit Plans Adjustment Including Portion Attributable to Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Defined Benefit Plans Adjustment Including Portion Attributable to Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Measurement Input Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input Type [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred income tax expense (benefit)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Income Tax Expense (Benefit)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Deferred Income Tax Expense (Benefit), Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financing Receivable, Allowance for Credit Losses [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Allowance for Credit Loss [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableGross_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Principal Amount Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableGross_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total Loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableGross_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investment securities, past due</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableGross_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Total Loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancialReceivablesPercentageOfTotalLoans_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Financial receivables percentage of total loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancialReceivablesPercentageOfTotalLoans_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Receivables Percentage of Total Loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancialReceivablesPercentageOfTotalLoans_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of total loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeasesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Leases [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeLiabilityCollateralRightToReclaimCashOffset_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Obligations secured with cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeLiabilityCollateralRightToReclaimCashOffset_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Liability, Subject to Master Netting Arrangement, Collateral, Right to Reclaim Cash Offset</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionOneMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Interest rate swap transaction one.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionOneMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Rate Swap Transaction One [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionOneMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest Rate Swap Transaction One [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableNonaccrualInterestIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest income on nonaccrual loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableNonaccrualInterestIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Nonaccrual, Interest Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UseOfEstimates_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Use of Estimates</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UseOfEstimates_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Use of Estimates, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CollateralizedMortgageObligationsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collateralized Mortgage Obligations [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CollateralizedMortgageObligationsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage Obligations [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromIssuanceOfLongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Proceeds from Issuance of Long-Term Debt, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromIssuanceOfLongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Issuance of Long-Term Debt</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromIssuanceOfLongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from long-term borrowings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfCollateralDependentLoansTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Collateral Dependent Loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfCollateralDependentLoansTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Collateral Dependent Loans Table [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfCollateralDependentLoansTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of collateral dependent loans.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StatementScenarioAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Scenario</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StatementScenarioAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Scenario [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestExpenseAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Noninterest expense:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestExpenseAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Noninterest Expense [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_SecurityExchangeName_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Security Exchange Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_SecurityExchangeName_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Security Exchange Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value by Liability Class</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value by Liability Class [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Financing Receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Financing Receivable [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_GainLossOnTaxCreditInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net gain on tax credit investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_GainLossOnTaxCreditInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Gain Loss On Tax Credit Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_GainLossOnTaxCreditInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Gain (loss) on tax credit investments.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashFlowHedgingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash Flow Hedge of Interest Rate Risk [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashFlowHedgingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Flow Hedging [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashFlowHedgingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Cash Flow Hedging [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cumulative Effect, Period of Adoption</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cumulative Effect, Period of Adoption [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementClassOfStockAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementClassOfStockAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Stock [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedFourYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prior Fiscal Year 4</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedFourYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeMaturityDates_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative, Contract End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeMaturityDates_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative, Contract End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueDisclosuresTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Measurements</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueDisclosuresTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Disclosures [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseLongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Long-term borrowings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseLongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Expense, Long-Term Debt</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseLongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Interest Expense, Long-term Debt, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialAssetPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Asset, Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialAssetPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MaximumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MaximumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Maximum [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total liabilities and shareholders&#8217; equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities and Equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due after five years through ten years, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net book value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease right of use assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Right-of-Use Asset</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Supplemental information:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Supplemental Cash Flow Information [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CompensationAndRetirementDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Retirement Benefits [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Diluted earnings per common share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share, Diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Earnings Per Share, Diluted, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Liabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Liabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesTreasuryStock_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Treasury shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesTreasuryStock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number of Shares, Treasury Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financing Receivable Recorded Investment [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Credit Quality Indicator [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss), before Reclassifications, before Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other comprehensive (loss) income, before Reclassifications, Pre-tax Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockGrantedDuringPeriodValueSharebasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock awards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockGrantedDuringPeriodValueSharebasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Shares Granted, Value, Share-Based Payment Arrangement, after Forfeiture</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockGrantedDuringPeriodValueSharebasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Hierarchy and NAV</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Hierarchy and NAV [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash provided by (used in) investing activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided by (Used in) Investing Activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_AddedWeightedAverageLoansLife_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Added weighted average loans life.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_AddedWeightedAverageLoansLife_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Added Weighted Average Loans Life</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_AddedWeightedAverageLoansLife_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Added Weighted Average Loans Life</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivableAfterDeferredIncomeOffsetAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivableAfterDeferredIncomeOffsetAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable After Deferred Income Offset Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivableAfterDeferredIncomeOffsetAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Financing receivable after deferred income offset amount.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeGainLossStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeGainLossStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSalesOfLoansNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Gain (Loss) on Sales of Loans, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSalesOfLoansNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Gain (Loss) on Sales of Loans, Net, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSalesOfLoansNet_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net gain on sale of loans held for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSalesOfLoansNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net gain on sale of loans held for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndDividendIncomeSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest and dividends on investment securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndDividendIncomeSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest and Dividend Income, Securities, Operating</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndDividendIncomeSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Interest and Dividend Income, Securities, Operating, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Off-Balance Sheet Commitments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Fair Value, off-Balance-Sheet Risks [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Financing Receivable Allowance For Credit Losses [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Allowance for Credit Loss [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeOperating_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Interest Income, Operating, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeOperating_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Income, Operating</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeOperating_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated interest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFilerCategory_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Filer Category</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFilerCategory_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Filer Category</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill and Other Intangible Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill and Intangible Assets Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Federal Home Loan Mortgage Corporation [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Financing Receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Financing Receivable [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassification Out Of Accumulated Other Comprehensive Income [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification out of Accumulated Other Comprehensive Income [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities Continuous Unrealized Loss Position Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">This item represents the fair value of securities which are in an unrealized loss position.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total AFS debt securities with unrealized losses, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivables30To59DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">30 to 59 Days Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivables30To59DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Asset, 30 to 59 Days Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InsuranceServicesRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Insurance income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InsuranceServicesRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Insurance Services Revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InsuranceServicesRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Insurance Services Revenue, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeNotionalAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Notional amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeNotionalAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross notional amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeNotionalAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative, Notional Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current Fiscal Year End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Current Fiscal Year End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Amounts representing interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, Undiscounted Excess Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueLiabilitiesLevel1ToLevel2TransferAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount of transfers of liabilities measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueLiabilitiesLevel1ToLevel2TransferAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Liabilities Level 1 to Level 2 Transfer Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueLiabilitiesLevel1ToLevel2TransferAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Level 1 to Level 2 transfers, liabilities amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Total share-based compensation expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-based compensation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Noncash Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Share-based Payment Arrangement, Noncash Expense, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoanRestructuringModificationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loan Restructuring Modification</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoanRestructuringModificationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loan Restructuring Modification [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetGross_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross carrying amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetGross_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Right Of Use Asset Gross</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetGross_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating lease right of use asset gross.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfBasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of basis of presentation and summary of significant accounting policies</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfBasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Basis of Presentation and Summary of Significant Accounting Policies [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityRegistrantName_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Registrant Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityRegistrantName_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Registrant Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromRecoveriesOfLoanPreviouslyChargedOff_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recovery of noninterest expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromRecoveriesOfLoanPreviouslyChargedOff_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds, Financing Receivable, Previously Written off, Recovery</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Securities available for sale, Unrealized Losses, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_StockReleasedDuringPeriodValueRestrictedStockUnits_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted stock units released</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_StockReleasedDuringPeriodValueRestrictedStockUnits_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Released During Period Value Restricted Stock Units</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_StockReleasedDuringPeriodValueRestrictedStockUnits_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Stock released during period value restricted stock units.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NumberOfReportableSegments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of reportable segments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NumberOfReportableSegments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Number of Reportable Segments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Earnings Per Common Share ("EPS")</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityEmergingGrowthCompany_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Emerging Growth Company</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityEmergingGrowthCompany_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Emerging Growth Company</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating Lease Liabilities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Liabilities [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating lease liabilities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Principal Amount Outstanding, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loan, Held-in-Portfolio, Principal Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeExtensibleEnumeration_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment, Type [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountingStandardsUpdate201613Member_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">ASU 2016-13 [Member]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total basic weighted average common shares outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number of Shares Outstanding, Basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investments [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StandbyLettersOfCreditMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Standby Letters Of Credit [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StandbyLettersOfCreditMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Standby Letters of Credit [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeLiabilityNotionalAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Liability, Notional Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllOtherSegmentsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">All Other [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllOtherSegmentsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Operating Segment [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesAuthorized_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, shares authorized</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesAuthorized_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Shares Authorized</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubleaseIncome_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Sublease income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubleaseIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Sublease Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Other comprehensive income (loss) before reclassifications</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other comprehensive income (loss), before Reclassifications, Net-of-tax Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss), before Reclassifications, Net of Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ValuationTechniqueAppraisalOfCollateralMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Appraisal of Collateral [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ValuationTechniqueAppraisalOfCollateralMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Valuation Technique Appraisal Of Collateral [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ValuationTechniqueAppraisalOfCollateralMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Valuation technique appraisal of collateral.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel1Member_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Level 1 Inputs [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel1Member_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Inputs, Level 1 [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfComprehensiveIncomeLossTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Comprehensive Income (Loss) [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfComprehensiveIncomeLossTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Components of Other Comprehensive (Loss) Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due from one to five years, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year One through Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Amortization expense during the year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amortization of intangibles</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Amortization of Intangible Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Amortization of Intangible Assets, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeAssetFairValueOfCollateral_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Asset, Fair Value of Collateral</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeAssetFairValueOfCollateral_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collateral on derivative instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Instruments Gain Loss By Hedging Relationship By Income Statement Location By Derivative Instrument Risk [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Instruments, Gain (Loss) [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialInstrumentAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Instrument</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialInstrumentAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Instrument [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of security positions, unrealized loss position</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities In Unrealized Loss Position Number Of Positions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of investments in securities measured at fair value with change in fair value and in unrealized loss position.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities Available-For-Sale and Transferred Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-Sale, Parent [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_AmountOfPreTaxLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount of pre tax loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_AmountOfPreTaxLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Amount of Pre Tax Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_AmountOfPreTaxLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Pre tax loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PassMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Uncriticized [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PassMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Pass [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestBearingDepositLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Noninterest-bearing demand</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestBearingDepositLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Noninterest-Bearing Deposit Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestBearingDepositLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Noninterest-bearing Deposit Liabilities, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComprehensiveIncomeNoteTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Other Comprehensive Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComprehensiveIncomeNoteTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Comprehensive Income (Loss) Note [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilitiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Liabilities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilitiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Liabilities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillImpairmentLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill, Impairment Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillImpairmentLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill impairment charge</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Components of Accumulated Other Comprehensive Income (Loss)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NumberOfBuildingsSubleased_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of buildings subleased</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NumberOfBuildingsSubleased_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Buildings Subleased</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NumberOfBuildingsSubleased_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of buildings subleased.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities available for sale, at fair value (amortized cost of $1,030,844 and $1,037,990, respectively)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Debt securities available for sale, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountingPoliciesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounting Policies [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Expense, Deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Interest Expense, Deposits, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestExpense_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Noninterest expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total noninterest expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Noninterest Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceCostCreditMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prior Service Credit [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceCostCreditMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shareholders&#8217; equity:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity, Attributable to Parent [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">This item represents the fair value of securities that have been in a continuous unrealized loss position for less than twelve months.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities, Less than 12 months, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total AFS debt securities with unrealized losses, Less than 12 months, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfInvestmentsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Investments [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfInvestmentsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Investments [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ShareholdersEquityTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shareholders Equity [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ShareholdersEquityTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Shareholders Equity [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ShareholdersEquityTable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Shareholders Equity [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DoubtfulMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Doubtful [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DoubtfulMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Doubtful [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Noncash investing and financing activities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Disposal Group Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statement [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due after five years through ten years, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, shares authorized</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Shares Authorized</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest expense:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Expense, Operating and Nonoperating [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFileNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity File Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFileNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Securities Act File Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Segment Reporting</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NonperformingFinancingReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-Performing [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NonperformingFinancingReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Nonperforming Financial Instruments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total reclassified for the period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedTotalLabel">Total reclassified for the period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Reclassification, Net of tax amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Amounts reclassified from accumulated other comprehensive income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net increase in cash and cash equivalents</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Earnings per common share (Note 2):</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Accrued interest receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued interest receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, after Year Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Thereafter</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiabilityStatementOfFinancialPositionExtensibleList_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating Lease, Liability, Statement of Financial Position [Extensible List]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiabilityStatementOfFinancialPositionExtensibleList_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Liability, Statement of Financial Position [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementOfFinancialPositionAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Financial Position [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total interest expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Expense, Operating and Nonoperating</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageBackedSecuritiesGovernmentNationalMortgageAssociationCertificatesAndObligationsGnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateralized Mortgage-Backed Securities Government National Mortgage Association Certificates and Obligations (GNMA).</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageBackedSecuritiesGovernmentNationalMortgageAssociationCertificatesAndObligationsGnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage-Backed Securities Government National Mortgage Association Certificates and Obligations (GNMA) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Asset</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative instruments, assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Derivative Asset, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityShellCompany_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Shell Company</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityShellCompany_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Shell Company</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccruedInvestmentIncomeReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued interest receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccruedInvestmentIncomeReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accrued Investment Income Receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccruedInvestmentIncomeReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Accrued Investment Income Receivable, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_BankingSegmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Banking [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_BankingSegmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Banking [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_BankingSegmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Banking Segment [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_BankingSegmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Banking Segment [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional Quantitative Information about Assets Measured at Fair Value on Recurring and Non-Recurring Basis</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement Inputs and Valuation Techniques [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityTaxIdentificationNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Tax Identification Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityTaxIdentificationNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Tax Identification Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">ASSETS</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Assets [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCurrentReportingStatus_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Current Reporting Status</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCurrentReportingStatus_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Current Reporting Status</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net income available to common shareholders</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net income available to common shareholders</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Net Income (Loss) Available to Common Stockholders, Basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ExtendedMaturityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Extended Maturity [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ExtendedMaturityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Extended Maturity [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Restricted stock awards forfeited</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period, Shares, Restricted Stock Award, Forfeited</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CardInterchangeIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Card interchange income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CardInterchangeIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Card Interchange Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CardInterchangeIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Card interchange income.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestIncomeOtherOperatingIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestIncomeOtherOperatingIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Noninterest Income, Other Operating Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentFiscalYearFocus_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Fiscal Year Focus</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentFiscalYearFocus_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Fiscal Year Focus</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockDividendsIncomeStatementImpact_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock dividends</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockDividendsIncomeStatementImpact_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Dividends, Income Statement Impact</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other than Temporary Impairment, Credit Losses Recognized in Earnings, Categories of Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other than Temporary Impairment, Credit Losses Recognized in Earnings, Categories of Investments [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total preferred equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Value, Issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Preferred Stock, Value, Issued, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Preferred Stock, Value, Issued, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Preferred Stock, Value, Issued, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansReceivableFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansReceivableFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loans Receivable, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Accumulated amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets, Accumulated Amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValueAcquiredCostMethod_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of common stock for treasury</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValueAcquiredCostMethod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Value, Acquired, Cost Method</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Cash and cash equivalents, beginning of period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Cash and cash equivalents, end of period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Securities Available For Sale And Held To Maturity Securities [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities Available For Sale And Held To Maturity Securities [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Debt securities available for sale and held to maturity securities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due from one to five years, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss), Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other comprehensive income (loss), Tax Effect</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CityAreaCode_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">City Area Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CityAreaCode_lbl" xlink:role="http://www.xbrl.org/2003/role/label">City Area Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PriorPeriodReclassificationAdjustmentDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassifications</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PriorPeriodReclassificationAdjustmentDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification, Comparability Adjustment [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_RetailLoanPortfolioCategorizedByPaymentStatusTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Retail Loan Portfolio Categorized by Performance Status</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_RetailLoanPortfolioCategorizedByPaymentStatusTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Retail Loan Portfolio Categorized By Payment Status Table [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_RetailLoanPortfolioCategorizedByPaymentStatusTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Retail Loan Portfolio Categorized By Payment Status [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfCashFlowSupplementalDisclosuresTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Supplemental Cash Flow Information</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfCashFlowSupplementalDisclosuresTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeContractTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Contract</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeContractTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Contract [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TroubledDebtRestructuringsOnFinancingReceivablesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Modified [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TroubledDebtRestructuringsOnFinancingReceivablesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amortized Cost basis of Loans Modified to Borrowers Experiencing Financial Difficulty</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableImpairedLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financing Receivable, Impaired [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableImpairedLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Impaired [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares of common stock authorized to be repurchased</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share Repurchase Program, Authorized, Number of Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSaleOfOtherAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net gain (loss) on other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSaleOfOtherAssets_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net gain on other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSaleOfOtherAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Gain (Loss) on Disposition of Other Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due after ten years, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_LocalPhoneNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Local Phone Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_LocalPhoneNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Local Phone Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating Lease Right of Use Assets:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Right Of Use Assets [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating lease right of use assets.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Business Segment Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reconciliation of Assets from Segment to Consolidated [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional paid-in capital</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Additional Paid in Capital</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Additional Paid in Capital, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Additional Paid in Capital, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Additional Paid in Capital, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale, Less than 12 months, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HedgingDesignationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Hedging Designation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HedgingDesignationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Hedging Designation [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount of accumulated pre-tax unrealized loss on securities that have been in a loss position for twelve months or longer.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities, 12 months or longer, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total AFS debt securities with unrealized losses, 12 months or longer, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SDNInsuranceAgencyLLCMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">S D N Insurance Agency L L C [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SDNInsuranceAgencyLLCMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">SDN Insurance Agency, LLC.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SDNInsuranceAgencyLLCMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">SDN [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitments and Contingencies Disclosure [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Treasury stock, at cost - 627,161 and 692,150 shares, respectively</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Treasury Stock, Value, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Treasury Stock, Value, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Treasury Stock, Value, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockAcquiredAverageCostPerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock repurchased average price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockAcquiredAverageCostPerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Shares Acquired, Average Cost Per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value By Balance Sheet Grouping [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, by Balance Sheet Grouping [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromRepaymentsOfShortTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net increase in short-term borrowings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromRepaymentsOfShortTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from (Repayments of) Short-Term Debt</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromRepaymentsOfShortTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Proceeds from (Repayments of) Short-term Debt, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFixedInterestRate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative fixed strike price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFixedInterestRate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative, Fixed Interest Rate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities available for sale, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Securities available for sale, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale, at fair value, amortized cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProfessionalFees_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Professional services</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProfessionalFees_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Professional Fees</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Retained Earnings [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Retained Earnings [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Defined Contribution Plan [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of premises and equipment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments to Acquire Property, Plant, and Equipment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Payments to Acquire Property, Plant, and Equipment, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentTransitionReport_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Transition Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentTransitionReport_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Transition Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepositsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Time deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepositsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deposits, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Decrease (increase) in other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Decrease (increase) in other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Increase (Decrease) in Other Operating Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Increase (Decrease) in Other Operating Assets, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndFeeIncomeLoansAndLeases_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest and fees on loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndFeeIncomeLoansAndLeases_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest and Fee Income, Loans and Leases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndFeeIncomeLoansAndLeases_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Interest and Fee Income, Loans and Leases, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ValuationTechniqueDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Valuation Approach and Technique</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ValuationTechniqueDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Valuation Approach and Technique [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Debt Securities Available For Sale and Held To Maturity Securities [Line Item]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities Available For Sale And Held To Maturity Securities [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Debt securities available for sale and held to maturity securities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Security, Excluded EPS Calculation [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due after five years through ten years, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansAndLeasesReceivableDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loans and Leases Receivable Disclosure [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialAssetNotPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Total Loans [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialAssetNotPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Asset, Not Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialAssetNotPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsHeldForSaleLongLivedFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Long-lived assets held for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsHeldForSaleLongLivedFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Long-Lived Asset, Held-for-Sale, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Past due greater than 90 days and still accruing interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, 90 Days or More Past Due, Still Accruing</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, Remainder of Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2024 (remainder of year)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MinimumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Minimum [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MinimumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Minimum [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_HeldToMaturitySecuritiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities held to maturity, at amortized cost (net of allowance for credit losses of $3 and $4, respectively) (fair value of $115,849 and $137,030, respectively)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_HeldToMaturitySecuritiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Held-to-maturity securities, net , Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_HeldToMaturitySecuritiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Held-to-maturity securities, net , Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_HeldToMaturitySecuritiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Held To Maturity Securities Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_HeldToMaturitySecuritiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Held-to-maturity securities, net.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Values of Derivative Instruments on the Balance Sheet</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional Paid-in Capital [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Additional Paid-in Capital [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillWrittenOffRelatedToSaleOfBusinessUnit_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reduction in carrying amount of goodwill</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillWrittenOffRelatedToSaleOfBusinessUnit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill, Written off Related to Sale of Business Unit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Adjustments to reconcile net income to net cash provided by operating activities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Maturities, Prepayments and Calls of Held-to-Maturity Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from principal payments, maturities and calls on held to maturity securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InformationTechnologyAndDataProcessing_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Computer and data processing</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InformationTechnologyAndDataProcessing_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Information Technology and Data Processing</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingSubleaseOptionToExtend_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sublease extension terms</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingSubleaseOptionToExtend_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Sublease, Option to Extend</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other comprehensive income (loss), net of tax:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss), Net of Tax [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueMeasurementWithUnobservableInputValuePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unobservable Input Value or Range</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueMeasurementWithUnobservableInputValuePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement With Unobservable Input Value Percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueMeasurementWithUnobservableInputValuePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Fair value measurement with unobservable input value percentage.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Statement Location</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Income Location, Balance [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommercialAndIndustrialMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commercial Business [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommercialAndIndustrialMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commercial And Industrial [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommercialAndIndustrialMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Commercial And Industrial [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionForCreditLossesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Provision for Credit Losses [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionForCreditLossesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Provision For Credit Losses [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionForCreditLossesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Provision for credit losses.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Segments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segments [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentDeferralMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferral [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentDeferralMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payment Deferral [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentDeferralMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Payment Deferral [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Increase (Decrease) in Other Operating Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Increase (Decrease) in Other Operating Liabilities, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Increase (decrease) in other liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Effect of Derivative Instruments on the Income Statement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Instruments, Gain (Loss) [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InformationByCategoryOfDebtSecurityAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Security Category</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InformationByCategoryOfDebtSecurityAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Security Category [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Proceeds from sales</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Sale of Debt Securities, Available-for-Sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">sales of securities -available for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill and Intangible Assets Disclosure [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financing Receivable, Recorded Investment, Past Due [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Past Due [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Common Stock, Shares Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Common Stock, Shares Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Accounts Notes Loans And Financing Receivable [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounts and Financing Receivables [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DerivativesEffectiveDate_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Derivatives effective date.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DerivativesEffectiveDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivatives Effective Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale, Less than 12 months, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoansAndLeasesReceivableDeferredLoanFeesCosts_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net Deferred Loan (Fees) Costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoansAndLeasesReceivableDeferredLoanFeesCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loans And Leases Receivable Deferred Loan Fees Costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoansAndLeasesReceivableDeferredLoanFeesCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Loans and leases receivable deferred loan (fees) costs.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoansAndLeasesReceivableDeferredLoanFeesCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net Deferred Loan (Fees) Costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basis of Presentation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Basis of Accounting, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, Year One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2025</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ScenarioUnspecifiedDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Scenario</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ScenarioUnspecifiedDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Scenario [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_TitleOfIndividualWithRelationshipToEntityDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Title of Individual</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_TitleOfIndividualWithRelationshipToEntityDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Title and Position [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Available for sale securities, allowance for credit loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Allowance for Credit Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Debt Securities, Available-for-sale, Allowance for Credit Loss, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Debt Securities, Available-for-sale, Allowance for Credit Loss, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Debt Securities, Available-for-sale, Allowance for Credit Loss, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, $0.01 par value; 50,000,000 shares authorized; 16,099,556 shares issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Value, Issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Common Stock, Value, Issued, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Common Stock, Value, Issued, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Common Stock, Value, Issued, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockDividendsPerShareDeclared_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock dividends per share, declared</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockDividendsPerShareDeclared_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Dividends Per Share, Declared</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleofFiniteLivedIntangibleAssetsFutureAmortizationExpenseTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated Amortization Expense of Other Intangible Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleofFiniteLivedIntangibleAssetsFutureAmortizationExpenseTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAociCurrentPeriodTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Reclassification, Tax Effect</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAociCurrentPeriodTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel">Reclassification tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAociCurrentPeriodTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Reclassification, Tax Effect</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAociCurrentPeriodTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification from AOCI, Current Period, Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAociCurrentPeriodTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassification tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash and cash equivalents</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash and Cash Equivalents, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TaxCreditInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Tax credit investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TaxCreditInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Tax Credit Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TaxCreditInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Tax credit investments.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockRepurchaseProgramRemainingNumberOfSharesAuthorizedToBeRepurchased_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Remaining shares of common stock authorized to be repurchased</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockRepurchaseProgramRemainingNumberOfSharesAuthorizedToBeRepurchased_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share Repurchase Program, Remaining Authorized, Number of Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextRollingTwelveMonths_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Next Rolling 12 Months</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextRollingTwelveMonths_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2024</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TroubledDebtRestructuringsOnFinancingReceivablesModificationEffectTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Troubled debt restructurings on financing receivables modification effect.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TroubledDebtRestructuringsOnFinancingReceivablesModificationEffectTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Troubled Debt Restructurings On Financing Receivables Modification Effect [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TroubledDebtRestructuringsOnFinancingReceivablesModificationEffectTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Effect of the Modifications Made to Borrowers Experiencing Financial Difficulty</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HomeEquityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Residential Real Estate Lines [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HomeEquityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Home Equity Line of Credit [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount of accumulated pre-tax unrealized loss on investments in securities that have been in a loss position for less than twelve months.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities, Less than 12 months, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total AFS debt securities with unrealized losses, Less than 12 months, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputConstantPrepaymentRateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Constant Prepayment Rate [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputConstantPrepaymentRateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input, Constant Prepayment Rate [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Present value of net future minimum operating lease payments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Operating Lease, Liability, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease right of use obligations</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Measurement Frequency</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Frequency [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Off-balance sheet commitments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitments and Contingencies</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherNoninterestExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherNoninterestExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Noninterest Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prior Fiscal Year 3</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale, 12 months or longer, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total diluted weighted average common shares outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number of Shares Outstanding, Diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total future minimum operating lease payments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due after ten years, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Weighted average common shares outstanding:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number of Shares Outstanding, Diluted [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Rolling Year Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2028</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubstandardMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Substandard [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubstandardMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Substandard [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntitySmallBusiness_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Small Business</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntitySmallBusiness_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Small Business</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingInformationLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Segment Reporting Information [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingInformationLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting Information [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoanServicingRightsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loan Servicing Rights [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoanServicingRightsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loan Servicing Rights [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoanServicingRightsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Loan servicing rights.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Federal National Mortgage Association [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities held to maturity, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Accumulated Unrecognized Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares issued in lieu of cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period, Shares, Issued for Services</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative instruments, liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Derivative Liability, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockSharesAcquired_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Treasury stock purchases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockSharesAcquired_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Shares, Acquired</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockSharesAcquired_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Treasury stock purchases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Carrying Amount, Estimated Fair Value, and Placement in Fair Value Hierarchy of Financial Instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, by Balance Sheet Grouping [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_IncrementalCommonSharesAttributableToVestingOfRestrictedStockAwards_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Vesting of restricted stock awards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_IncrementalCommonSharesAttributableToVestingOfRestrictedStockAwards_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Incremental Common Shares Attributable To Vesting Of Restricted Stock Awards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_IncrementalCommonSharesAttributableToVestingOfRestrictedStockAwards_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Incremental common shares attributable to vesting of restricted stock awards.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsMiscellaneous_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other Assets, Miscellaneous, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsMiscellaneous_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsMiscellaneous_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets, Miscellaneous</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due after ten years, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfShareBasedCompensationRestrictedStockUnitsAndPerformanceShareUnitsActivityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Restricted Stock Awards ,Restricted Stock Unit Award and Performance Share Units Activity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfShareBasedCompensationRestrictedStockUnitsAndPerformanceShareUnitsActivityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Share Based Compensation Restricted Stock Units And Performance Share Units Activity Table [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfShareBasedCompensationRestrictedStockUnitsAndPerformanceShareUnitsActivityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of Share-based Compensation, Restricted Stock Units and Performance Share Units Activity [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accretion (Amortization) of Discounts and Premiums, Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net amortization of premiums on securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due from one to five years, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Deposits_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Deposits_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock awards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period, Shares, Treasury Stock Reissued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from financing activities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Net Cash Provided by (Used in) Financing Activities [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnusualOrInfrequentItemAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unusual or Infrequent Item, or Both</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnusualOrInfrequentItemAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Unusual or Infrequent Item, or Both [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercise of stock options</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Incremental Common Shares Attributable to Share-based Payment Arrangements, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByAssetClassAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Asset Class</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByAssetClassAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Asset Class [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Instruments and Hedging Activities Disclosure [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SeriesAThreePercentagePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series A 3% Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SeriesAThreePercentagePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Series A Three Percentage Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SeriesAThreePercentagePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Series A three percentage Preferred Stock.</link:label>
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  <xsd:element id="fisi_LoansAndLeasesReceivableDeferredLoanFeesCosts" name="LoansAndLeasesReceivableDeferredLoanFeesCosts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_NoninterestIncomeLoanServicing" name="NoninterestIncomeLoanServicing" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_ValuationTechniqueAppraisalOfCollateralMember" name="ValuationTechniqueAppraisalOfCollateralMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_AddedWeightedAverageLoansLife" name="AddedWeightedAverageLoansLife" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_NoninterestIncomeInvestmentsInLimitedPartnerships" name="NoninterestIncomeInvestmentsInLimitedPartnerships" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_IncrementalCommonSharesAttributableToVestingOfRestrictedStockAwards" name="IncrementalCommonSharesAttributableToVestingOfRestrictedStockAwards" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesLineItems" name="DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_CollateralizedMortgageObligationsFederalHomeLoanMortgageCorporationCertificatesAndObligationsFhlmcMember" name="CollateralizedMortgageObligationsFederalHomeLoanMortgageCorporationCertificatesAndObligationsFhlmcMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_FinancingReceivableAfterDeferredIncomeOffsetAmount" name="FinancingReceivableAfterDeferredIncomeOffsetAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_InvestmentSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" name="InvestmentSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_CollateralizedMortgageObligationsGovernmentNationalMortgageAssociationCertificatesAndObligationsGnmaMember" name="CollateralizedMortgageObligationsGovernmentNationalMortgageAssociationCertificatesAndObligationsGnmaMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_TroubledDebtRestructuringsOnFinancingReceivablesPerformanceOfLoansTableTextBlock" name="TroubledDebtRestructuringsOnFinancingReceivablesPerformanceOfLoansTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_GainLossOnDispositionOfOtherAssets" name="GainLossOnDispositionOfOtherAssets" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_CollateralDependentLoansOnBusinessAssets" name="CollateralDependentLoansOnBusinessAssets" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_ScheduleOfShareBasedCompensationRestrictedStockUnitsAndPerformanceShareUnitsActivityTableTextBlock" name="ScheduleOfShareBasedCompensationRestrictedStockUnitsAndPerformanceShareUnitsActivityTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_CardInterchangeIncome" name="CardInterchangeIncome" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_NoninterestIncomeServiceChargesOnDeposits" name="NoninterestIncomeServiceChargesOnDeposits" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_ShareholdersEquityLineItems" name="ShareholdersEquityLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_FraudulentActivityPolicyTextBlock" name="FraudulentActivityPolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_DirectorStockIncentivePlanMember" name="DirectorStockIncentivePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_DerivativesEffectiveDate" name="DerivativesEffectiveDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_InvestmentSecuritiesAccumulatedUnrecognizedHoldingLoss" name="InvestmentSecuritiesAccumulatedUnrecognizedHoldingLoss" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_CollateralDependentLoans" name="CollateralDependentLoans" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_InterestRateSwapTransactionThreeMember" name="InterestRateSwapTransactionThreeMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_ConsumerIndirectMember" name="ConsumerIndirectMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_FinancingReceivables30To89DaysPastDueMember" name="FinancingReceivables30To89DaysPastDueMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_PaymentsForProceedsFromLifeInsurancePolicies1" name="PaymentsForProceedsFromLifeInsurancePolicies1" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_AllowanceForCreditLossesAmortizedCost" name="AllowanceForCreditLossesAmortizedCost" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_TroubledDebtRestructuringsOnFinancingReceivablesModificationEffectTableTextBlock" name="TroubledDebtRestructuringsOnFinancingReceivablesModificationEffectTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" name="InvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_ScheduleOfLeaseCostsAndOtherLeaseInformationTableTextBlock" name="ScheduleOfLeaseCostsAndOtherLeaseInformationTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_ProvisionForCreditLosses" name="ProvisionForCreditLosses" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_StockReleasedDuringPeriodSharesRestrictedStockUnits" name="StockReleasedDuringPeriodSharesRestrictedStockUnits" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_NonMaturityDepositsFairValueDisclosure" name="NonMaturityDepositsFairValueDisclosure" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_ConsumerOverdraftsMember" name="ConsumerOverdraftsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_LongLivedAssetsHeldForSaleMember" name="LongLivedAssetsHeldForSaleMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesTable" name="DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_FairValueLiabilitiesLevel1ToLevel2TransferAmount" name="FairValueLiabilitiesLevel1ToLevel2TransferAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_TaxCreditInvestments" name="TaxCreditInvestments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_CollateralizedMortgageBackedSecuritiesFederalHomeLoanMortgageCorporationCertificatesAndObligationsFhlmcMember" name="CollateralizedMortgageBackedSecuritiesFederalHomeLoanMortgageCorporationCertificatesAndObligationsFhlmcMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_ManagementStockIncentivePlanMember" name="ManagementStockIncentivePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_AmountOfPreTaxLoss" name="AmountOfPreTaxLoss" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_GainOnDivestitureOfInterestInConsolidatedSubsidiaries" name="GainOnDivestitureOfInterestInConsolidatedSubsidiaries" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_CommitmentsAndContingenciesLineItems" name="CommitmentsAndContingenciesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_InterestRateSwapTransactionOneMember" name="InterestRateSwapTransactionOneMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_CurrentPeriodGrossWriteOffsMember" name="CurrentPeriodGrossWriteOffsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_FinancingReceivableAllowanceForLoanLossesProvisionCredit" name="FinancingReceivableAllowanceForLoanLossesProvisionCredit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_BankingSegmentMember" name="BankingSegmentMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue" name="InvestmentSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_VestedImmediatelyMember" name="VestedImmediatelyMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_ScheduleOfClassificationOfRightOfUseAssetsAndLeaseLiabilitiesTableTextBlock" name="ScheduleOfClassificationOfRightOfUseAssetsAndLeaseLiabilitiesTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_CollateralizedMortgageObligationsFederalNationalMortgageAssociationCertificatesAndObligationsFnmaMember" name="CollateralizedMortgageObligationsFederalNationalMortgageAssociationCertificatesAndObligationsFnmaMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_CollateralDependentLoanWithSpecificReserve" name="CollateralDependentLoanWithSpecificReserve" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_FairValueAssetsLevel1ToLevel2TransferAmount" name="FairValueAssetsLevel1ToLevel2TransferAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_OtherLiabilitiesMiscellaneous" name="OtherLiabilitiesMiscellaneous" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_CommitmentsAndContingenciesTable" name="CommitmentsAndContingenciesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_ScheduleOfBasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTable" name="ScheduleOfBasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_InternallyRatedHeldToMaturitySecurities" name="InternallyRatedHeldToMaturitySecurities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_ProvisionBenefitForCreditLosses" name="ProvisionBenefitForCreditLosses" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_SeriesAThreePercentagePreferredStockMember" name="SeriesAThreePercentagePreferredStockMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_SalariesAndEmployeeBenefitsMember" name="SalariesAndEmployeeBenefitsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_SeriesB1EightPointFourEightPercentagePreferredStockMember" name="SeriesB1EightPointFourEightPercentagePreferredStockMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_OtherRealEstateOwnedOtherReceivableMember" name="OtherRealEstateOwnedOtherReceivableMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_FraudActivityMember" name="FraudActivityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_ScheduleOfCreditLossExpenseBenefitForUnfundedCommitmentsTableTextBlock" name="ScheduleOfCreditLossExpenseBenefitForUnfundedCommitmentsTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_InterestRateSwapTransactionTwoMember" name="InterestRateSwapTransactionTwoMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_HeldToMaturitySecuritiesNet" name="HeldToMaturitySecuritiesNet" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_CollateralDependentFinancingReceivableMember" name="CollateralDependentFinancingReceivableMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_FairValueMeasurementWithUnobservableInputValuePercentage" name="FairValueMeasurementWithUnobservableInputValuePercentage" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_InvestmentSecuritiesInUnrealizedLossPositionsTwelveMonthsOrLongerQualitativeDisclosureNumberOfPositions" name="InvestmentSecuritiesInUnrealizedLossPositionsTwelveMonthsOrLongerQualitativeDisclosureNumberOfPositions" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="fisi_NatureOfBusinessOperationsPolicyTextBlock" name="NatureOfBusinessOperationsPolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_PerformanceShareUnitsMember" name="PerformanceShareUnitsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_DepositRelatedChargedOffItems" name="DepositRelatedChargedOffItems" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_FinancialReceivablesPercentageOfTotalLoans" name="FinancialReceivablesPercentageOfTotalLoans" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="fisi_OtherAssetsAndOtherLiabilitiesDisclosureTextBlock" name="OtherAssetsAndOtherLiabilitiesDisclosureTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_CollateralizedMortgageBackedSecuritiesGovernmentNationalMortgageAssociationCertificatesAndObligationsGnmaMember" name="CollateralizedMortgageBackedSecuritiesGovernmentNationalMortgageAssociationCertificatesAndObligationsGnmaMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_ReturnOnAverageAssetsPerformanceRequirementMember" name="ReturnOnAverageAssetsPerformanceRequirementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_CurrentMember" name="CurrentMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_RetailLoanPortfolioCategorizedByPaymentStatusTableTextBlock" name="RetailLoanPortfolioCategorizedByPaymentStatusTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_ProvisionForCreditLossesMember" name="ProvisionForCreditLossesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_ReturnOnAverageEquityMember" name="ReturnOnAverageEquityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_LoansHeldForSaleMember" name="LoansHeldForSaleMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
</xsd:schema>
