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

    <schemaVersion>X0609</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2026-07-10</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0000895574</issuerCik>
        <issuerName>abrdn National Municipal Income Fund</issuerName>
        <issuerTradingSymbol>VFL</issuerTradingSymbol>
        <issuerForeignTradingSymbol></issuerForeignTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001817331</rptOwnerCik>
            <rptOwnerName>Reit Todd</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerNonUSAddressFlag>false</rptOwnerNonUSAddressFlag>
            <rptOwnerStreet1>C/O ABRDN</rptOwnerStreet1>
            <rptOwnerStreet2>1900 MARKET STREET, SUITE 200</rptOwnerStreet2>
            <rptOwnerCity>PHILADELPHIA</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19103</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2026-07-10</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1298</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>11.3116</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Effective as of July 10, 2026, abrdn National Municipal Income Fund (the &quot;Target Fund&quot;) was reorganized into the Aberdeen Municipal Income Fund. (the &quot;Acquiring Fund,&quot; and such reorganization, the &quot;Reorganization&quot;). In the Reorganization, common shareholders of the Target Fund received common shares of the Acquiring Fund having a value equal to the aggregate NAV of the Target Fund common shares surrendered as determined at the close of business on July 10, 2026, less the costs of the Reorganization (although cash was distributed for any fractional shares). As of July 10, 2026, the Target Fund reported a NAV per share of $11.3116 and the Acquiring Fund reported a NAV per share of $6.0322. The conversion ratio for the Target Fund's common shares was 1.87521869. In the Reorganization, the Reporting Person received 2,434 common shares of the Acquiring Fund in exchange for their 1,298 common shares of the Target Fund.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Robert Stieger, by POA from Reporting Person</signatureName>
        <signatureDate>2026-07-14</signatureDate>
    </ownerSignature>
</ownershipDocument>
