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

    <schemaVersion>X0203</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2010-11-16</periodOfReport>

    <noSecuritiesOwned>1</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001071264</issuerCik>
        <issuerName>JACKSONVILLE BANCORP INC /FL/</issuerName>
        <issuerTradingSymbol>JAXB</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001505877</rptOwnerCik>
            <rptOwnerName>CapGen Capital Group IV LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>280 PARK AVENUE, 40TH FLOOR WEST</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 401</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10017</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>See Remarks</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001505878</rptOwnerCik>
            <rptOwnerName>CapGen Capital Group IV LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>280 PARK AVENUE WEST</rptOwnerStreet1>
            <rptOwnerStreet2>WEST 40TH FLOOR SUITE 401</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10017</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001453863</rptOwnerCik>
            <rptOwnerName>Ludwig Eugene</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>280 PARK AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>40TH FLOOR WEST SUITE 401</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10017</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes></footnotes>

    <remarks>Pursuant to the Stock Purchase Agreement, dated as of May 10, 2010 (as amended), among Jacksonville Bancorp, Inc. (the &quot;Issuer&quot;), CapGen Capital Group IV LP (&quot;CapGen LP&quot;) and the other investors party thereto, CapGen LP has the right to designate, and has designated, two members to the board of directors of the Issuer (Messrs. John Rose and John Sullivan). CapGen Capital Group IV LLC (&quot;CapGen LLC&quot;) is the sole general partner of CapGen LP. Mr. Eugene A. Ludwig is the managing member of CapGen LLC. CapGen LP, CapGen LLC and Mr. Ludwig disclaim their possible status as directors of the Issuer by deputization by virtue of Messrs. Rose and Sullivan's positions as members of the board of directors of the Issuer.</remarks>

    <ownerSignature>
        <signatureName>/s/ Eugene A. Ludwig, the managing member of CapGen Capital Group IV LLC, the general partner of CapGen Capital Group IV LP</signatureName>
        <signatureDate>2010-11-17</signatureDate>
    </ownerSignature>
</ownershipDocument>
