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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2013-04-04</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000024751</issuerCik>
        <issuerName>CORNING NATURAL GAS CORP</issuerName>
        <issuerTradingSymbol>CNIG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001327004</rptOwnerCik>
            <rptOwnerName>Mirabito Joseph P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O THE WILBER CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>245 MAIN STREET, PO BOX 430</rptOwnerStreet2>
            <rptOwnerCity>ONEONTA</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>13820</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2013-04-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>700</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>15.49</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>42549</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F1"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>see note</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Includes 3,427 shares of restricted stock and 1,999 shares held by Mr. Mirabito's wife. Mr. Mirabito disclaims beneficial ownership of the securities owned by his wife except to the extent of his pecuniary interest therein. Also includes 37,085 of the 185,425 shares of common stock owned by Mirabito Holdings, Inc. Mr. Mirabito is the Chief Executive Officer of Mirabito Holdings, Inc. and holds a 20% ownership interest in the corporation.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Stanley G. Sleve, Attorney in Fact for Joseph P. Mirabito</signatureName>
        <signatureDate>2013-04-09</signatureDate>
    </ownerSignature>
</ownershipDocument>
