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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-10-10</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001432141</rptOwnerCik>
            <rptOwnerName>Rosenbluth Hal F.</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>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Senior Vice President</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Walgreen Co. Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-10-10</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>10000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>23.98</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>21789</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Walgreen Co. Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote.</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Weighted average purchase price.  Purchases executed from $23.91 to $24.04 per share.  The reporting person undertakes to provide upon request by SEC staff, the issuer, or any security holder of the issuer, full information regarding the number of shares purchased at each separate price.</footnote>
        <footnote id="F2">Shares held in custodial account for the benefit of the reporting person's child under the Uniform Transfer to Minors Act.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Yuri Rozenfeld, attorney-in-fact</signatureName>
        <signatureDate>2008-10-14</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0303
4
2008-10-10
0000104207
WALGREEN CO
WAG
0001432141
Rosenbluth Hal F.
WALGREEN CO.
200 WILMOT ROAD
DEERFIELD
IL
60015
0
1
0
0
Senior Vice President
Walgreen Co. Common Stock
2008-10-10
4
P
0
10000
23.98
A
21789
D
Walgreen Co. Common Stock
10
I
See footnote.
Weighted average purchase price.  Purchases executed from $23.91 to $24.04 per share.  The reporting person undertakes to provide upon request by SEC staff, the issuer, or any security holder of the issuer, full information regarding the number of shares purchased at each separate price.
Shares held in custodial account for the benefit of the reporting person's child under the Uniform Transfer to Minors Act.
Yuri Rozenfeld, attorney-in-fact
2008-10-14