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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 FgASttTr2hVzzVfbqwMfDVKFH8jb1QKqA8Gw7uLC0b7VNxlazaJ6+jwq7x02KE47
 z3I57TBlyb8TroSUFBpqdg==

<SEC-DOCUMENT>0001450556-09-000009.txt : 20090223
<SEC-HEADER>0001450556-09-000009.hdr.sgml : 20090223
<ACCEPTANCE-DATETIME>20090223171134
ACCESSION NUMBER:		0001450556-09-000009
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20090220
FILED AS OF DATE:		20090223
DATE AS OF CHANGE:		20090223

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Investors Bancorp Inc
		CENTRAL INDEX KEY:			0001326807
		STANDARD INDUSTRIAL CLASSIFICATION:	SAVINGS INSTITUTION, FEDERALLY CHARTERED [6035]
		IRS NUMBER:				223493930
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			0630

	BUSINESS ADDRESS:	
		STREET 1:		101 JFK PARKWAY
		CITY:			SHORT HILLS
		STATE:			NJ
		ZIP:			07078
		BUSINESS PHONE:		800-252-8119

	MAIL ADDRESS:	
		STREET 1:		101 JFK PARKWAY
		CITY:			SHORT HILLS
		STATE:			NJ
		ZIP:			07078

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Petroski Richard J
		CENTRAL INDEX KEY:			0001437678

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-51557
		FILM NUMBER:		09628756

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		(973) 924-5100

	MAIL ADDRESS:	
		STREET 1:		101 JFK PARKWAY
		CITY:			SHORT HILLS
		STATE:			NJ
		ZIP:			07078
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-02-20</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001326807</issuerCik>
        <issuerName>Investors Bancorp Inc</issuerName>
        <issuerTradingSymbol>ISBC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001437678</rptOwnerCik>
            <rptOwnerName>Petroski Richard J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>101 JFK PARKWAY</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SHORT HILLS</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07078</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>2009-02-20</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>7.16</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <ownerSignature>
        <signatureName>Thomas Splaine Jr, pursuant to power of attorney</signatureName>
        <signatureDate>2009-02-23</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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