<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0607</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2026-09-15</periodOfReport>

    <noSecuritiesOwned>1</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000357301</issuerCik>
        <issuerName>TRUSTCO BANK CORP N Y</issuerName>
        <issuerTradingSymbol>TRST</issuerTradingSymbol>
        <issuerForeignTradingSymbol></issuerForeignTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0002156702</rptOwnerCik>
            <rptOwnerName>Guentner Bryan Lee</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerNonUSAddressFlag>false</rptOwnerNonUSAddressFlag>
            <rptOwnerStreet1>C/O TRUSTCO BANK CORP NY</rptOwnerStreet1>
            <rptOwnerStreet2>5 SARNOWSKI DRIVE</rptOwnerStreet2>
            <rptOwnerCity>GLENVILLE</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>12302</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>true</isDirector>
            <isOfficer>false</isOfficer>
            <isTenPercentOwner>false</isTenPercentOwner>
            <isOther>false</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <footnotes></footnotes>

    <ownerSignature>
        <signatureName>/s/MICHAEL M. OZIMEK, BY POWER OF ATTORNEY</signatureName>
        <signatureDate>2026-09-24</signatureDate>
    </ownerSignature>
</ownershipDocument>
