If you are filing Form 8379 by itself, and you filed your joint tax return by mail, mail Form 8379 to the same address where you mailed your tax return. If you are filing Form 8379 by itself, you e-filed your joint tax return, and you live in Michigan, mail Form 8379 to the following address.

Department of the Treasury
Internal Revenue Service
Fresno, CA  93888-0002

If you are filing Form 8379 by itself, note the following from the IRS instructions for Form 8379.

"If you file Form 8379 separately, please be sure to attach a copy of all Forms W-2 and W-2G for both spouses, and any Forms 1099 showing federal income tax withholding, to Form 8379. The processing of Form 8379 may be delayed if these forms are not attached, if the form is incomplete when filed, or if you attach a copy of your joint tax return."