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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2014-08-29</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000101199</issuerCik>
        <issuerName>UNITED FIRE GROUP INC</issuerName>
        <issuerTradingSymbol>UFCS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001451184</rptOwnerCik>
            <rptOwnerName>SCHARMER NEAL R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>118 SECOND AVENUE SE</rptOwnerStreet1>
            <rptOwnerStreet2>P.O. BOX 73909</rptOwnerStreet2>
            <rptOwnerCity>CEDAR RAPIDS</rptOwnerCity>
            <rptOwnerState>IA</rptOwnerState>
            <rptOwnerZipCode>52407-3909</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>VP/General Counsel/Corp Sec</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2014-08-29</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value>E</value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>6</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>29.32</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>876</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Issuer's 401(k) Plan for Self</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Shares acquired through standard payroll deduction and participation in Issuer's 401(k) Plan.</footnote>
        <footnote id="F2">Represents the approximate number of shares (excluding fractionals) acquired by the trustee/administrator of the Issuer's 401(k)Plan for the Reporting Person's benefit, based on a statement of the plan trustee/administrator.</footnote>
        <footnote id="F3">The number of securities shown as being held in or acquired by the Issuer's 401(k) account for the Reporting Person's benefit are the approximate number of shares of Issuer common stock(excluding fractionals) for which the Reporting Person has the right to direct the vote under the Issuer's 401(k) Plan. Such shares are not directly allocated to 401(k) Plan participants, but are instead held in a unitized fund consisting primarily of Issuer common stock, together with a small percentage of short-term investments. 401(k) Plan participants acquire units of this fund.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Neal R. Scharmer by Dianne M. Lyons, Attorney-in-Fact</signatureName>
        <signatureDate>2014-09-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2014-08-29
0
0000101199
UNITED FIRE GROUP INC
UFCS
0001451184
SCHARMER NEAL R
118 SECOND AVENUE SE
P.O. BOX 73909
CEDAR RAPIDS
IA
52407-3909
0
1
0
0
VP/General Counsel/Corp Sec
Common Stock
2014-08-29
5
J
0
E
6
29.32
A
876
I
By Issuer's 401(k) Plan for Self
Shares acquired through standard payroll deduction and participation in Issuer's 401(k) Plan.
Represents the approximate number of shares (excluding fractionals) acquired by the trustee/administrator of the Issuer's 401(k)Plan for the Reporting Person's benefit, based on a statement of the plan trustee/administrator.
The number of securities shown as being held in or acquired by the Issuer's 401(k) account for the Reporting Person's benefit are the approximate number of shares of Issuer common stock(excluding fractionals) for which the Reporting Person has the right to direct the vote under the Issuer's 401(k) Plan. Such shares are not directly allocated to 401(k) Plan participants, but are instead held in a unitized fund consisting primarily of Issuer common stock, together with a small percentage of short-term investments. 401(k) Plan participants acquire units of this fund.
/s/ Neal R. Scharmer by Dianne M. Lyons, Attorney-in-Fact
2014-09-04