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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-12-12</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0000104207</issuerCik>
        <issuerName>WALGREEN CO</issuerName>
        <issuerTradingSymbol>WAG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001197070</rptOwnerCik>
            <rptOwnerName>FERSTEL MARILOU VON</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>WALGREEN CO.</rptOwnerStreet1>
            <rptOwnerStreet2>200 WILMOT ROAD</rptOwnerStreet2>
            <rptOwnerCity>DEERFIELD</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60015</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Dividend Equivalent Rights</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2009-12-12</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>26.1793</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>38.81</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>26.1793</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>26.1793</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The dividend equivalent rights convert into the cash value of the company's common stock on a one-for-one basis.</footnote>
        <footnote id="F2">Shares issued under the Walgreen Co. Nonemployee Director Stock Plan.</footnote>
        <footnote id="F3">To be settled in two installments, the first of which occurs within thirty days following termination of service as a director, and the second, one year after the first settlement date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Yuri Rozenfeld, Attorney-in-Fact</signatureName>
        <signatureDate>2010-01-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0303
4
2009-12-12
1
0000104207
WALGREEN CO
WAG
0001197070
FERSTEL MARILOU VON
WALGREEN CO.
200 WILMOT ROAD
DEERFIELD
IL
60015
1
0
0
0
Dividend Equivalent Rights
2009-12-12
5
A
0
26.1793
38.81
A
Common Stock
26.1793
26.1793
D
The dividend equivalent rights convert into the cash value of the company's common stock on a one-for-one basis.
Shares issued under the Walgreen Co. Nonemployee Director Stock Plan.
To be settled in two installments, the first of which occurs within thirty days following termination of service as a director, and the second, one year after the first settlement date.
/s/ Yuri Rozenfeld, Attorney-in-Fact
2010-01-19