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

    <schemaVersion>X0508</schemaVersion>

    <documentType>5</documentType>

    <periodOfReport>2026-01-03</periodOfReport>

    <notSubjectToSection16>false</notSubjectToSection16>

    <form3HoldingsReported>0</form3HoldingsReported>

    <form4TransactionsReported>0</form4TransactionsReported>

    <issuer>
        <issuerCik>0000031107</issuerCik>
        <issuerName>EASTERN CO</issuerName>
        <issuerTradingSymbol>EML</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001964629</rptOwnerCik>
            <rptOwnerName>Vlahos Nicholas Alec</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3 ENTERPRISE DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 408</rptOwnerStreet2>
            <rptOwnerCity>SHELTON</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06484</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>false</isDirector>
            <isOfficer>true</isOfficer>
            <isTenPercentOwner>false</isTenPercentOwner>
            <officerTitle>Chief Financial Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>false</aff10b5One>

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                <value>Common Shares</value>
                <footnoteId id="F1"/>
            </securityTitle>
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            </transactionDate>
            <transactionCoding>
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                <transactionCode>L</transactionCode>
                <equitySwapInvolved>false</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
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                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
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                </directOrIndirectOwnership>
            </ownershipNature>
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            <securityTitle>
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                <footnoteId id="F1"/>
            </securityTitle>
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                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
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                </transactionAcquiredDisposedCode>
            </transactionAmounts>
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                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
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            </ownershipNature>
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                </transactionPricePerShare>
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                </transactionPricePerShare>
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                </sharesOwnedFollowingTransaction>
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                <value>Common Shares</value>
                <footnoteId id="F1"/>
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                <transactionFormType>5</transactionFormType>
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                    <value>A</value>
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                <transactionAcquiredDisposedCode>
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                <transactionCode>P</transactionCode>
                <equitySwapInvolved>false</equitySwapInvolved>
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        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
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                <footnoteId id="F1"/>
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            <transactionDate>
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                <transactionFormType>5</transactionFormType>
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                <equitySwapInvolved>false</equitySwapInvolved>
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                <transactionShares>
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                <transactionPricePerShare>
                    <value>19.22</value>
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    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Shares acquired under the Eastern Company Investor Choice Dividend Reinvestment and Director Stock Purchase Sale Plan.</footnote>
        <footnote id="F2">Represents shares acquired by the reporting person through the reinvestment of dividends under the Eastern Company Investors Choice Dividend Reinvestment and Direct Stock Purchase Sale Plan.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Nicholas A. Vlahos</signatureName>
        <signatureDate>2026-01-13</signatureDate>
    </ownerSignature>
</ownershipDocument>
