<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>
<periodOfReport>2003-08-29</periodOfReport>
<notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000785024</issuerCik>
        <issuerName>MID WISCONSIN FINANCIAL SERVICES INC</issuerName>
        <issuerTradingSymbol>MWFS</issuerTradingSymbol>
</issuer>
<reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001186777</rptOwnerCik>
            <rptOwnerName>MERTENS KURT D</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O MID-WISCONSIN BANK</rptOwnerStreet1>
            <rptOwnerStreet2>PO BOX 90</rptOwnerStreet2>
            <rptOwnerCity>MEDFORD</rptOwnerCity>
            <rptOwnerState>WI</rptOwnerState>
            <rptOwnerZipCode>54451</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector>
<isOfficer>0</isOfficer>
<isTenPercentOwner>0</isTenPercentOwner>
<isOther>0</isOther>
<officerTitle></officerTitle>
<otherText></otherText>
</reportingOwnerRelationship>
</reportingOwner>
<derivativeTable>
<derivativeTransaction>
<securityTitle>
<value>Common stock equivalent units</value>
</securityTitle>
<conversionOrExercisePrice>
<value>30.53</value>
</conversionOrExercisePrice>
<transactionDate>
<value>2003-08-29</value>
</transactionDate>
<deemedExecutionDate>
</deemedExecutionDate>
<transactionCoding>
<transactionFormType>4</transactionFormType>
<transactionCode>A</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved>
</transactionCoding>
<transactionTimeliness>
<value></value>
</transactionTimeliness>
<transactionAmounts>
<transactionShares>
<value>14.412</value>
</transactionShares>
<transactionPricePerShare>
<value>30.53</value>
</transactionPricePerShare>
<transactionAcquiredDisposedCode>
<value>A</value>
</transactionAcquiredDisposedCode>
</transactionAmounts>
<exerciseDate>
<value>2020-09-30</value>
</exerciseDate>
<expirationDate>
<value>2020-09-30</value>
</expirationDate>
<underlyingSecurity>
<underlyingSecurityTitle>
<value>Common stock</value>
</underlyingSecurityTitle>
<underlyingSecurityShares>
<value>14.412</value>
</underlyingSecurityShares>
</underlyingSecurity>
<postTransactionAmounts>
<sharesOwnedFollowingTransaction>
<value>693.3854</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature>
<directOrIndirectOwnership>
<value>D</value>
</directOrIndirectOwnership>
<natureOfOwnership>
<value></value>
</natureOfOwnership>
</ownershipNature>
</derivativeTransaction>
</derivativeTable>
<remarks>(1) Stocks equivalent units accrued under Mid-Wisconsin Financial Services, Inc </remarks>
<ownerSignature>
<signatureName>Kurt D Mertens / Gene C Knoll</signatureName>
<signatureDate>2003-09-03</signatureDate>
</ownerSignature>
</ownershipDocument>

