What federal forms must I attach to my IL-1120?

When filing your return there are certain types of income items and subtraction modifications that require the attachment of Illinois or federal forms and schedules. Instructions for these attachments appear throughout the specific Form IL-1120 instructions for completing your return.

All taxpayers, including unitary business groups, must attach a copy of all pages of U.S. Form 1120, and Schedules L, M-1, M-2, and M-3, if applicable, to your Illinois return. However, there are a few exceptions:

  • If you are a corporation, but do not file U.S. Form 1120, you must attach a copy of the form that you file federally, including, U.S. Form 1120-L, Page 1, or U.S. Form 1120-PC, Page 1 (and Schedule A, if filed), 1120-POL, 1120-H, or 1120-SF.
  • If you are a corporation whose taxable income is included in a consolidated federal tax return, you must provide a pro forma copy of U.S. Form 1120, U.S. Form 1120-L, or U.S. Form 1120-PC, and all applicable schedules as if you had filed a separate federal return.

Note: When filing your Form IL-1120, Corporation Income and Replacement Tax Return, include only forms and schedules required to support your return. Please do not attach correspondence to your return.

If you have additional inquiries, you may submit them to the Questions, Comments, or Request form.