Who must file Form IL-1120-ST

You must file Form IL-1120-ST, Small Business Corporation Replacement Tax Return, if you are a small business corporation (S corp), as defined in Internal Revenue Code (IRC), Section 1361(a), that

  • has net income or loss as defined under the Illinois Income Tax Act (IITA) or 
  • is qualified to do business in the state of Illinois and is required to file U.S. Form 1120S (regardless of net income or loss).

You are required to report and pay pass-through withholding on behalf of your nonresident shareholders if they have not provided Form IL-1000-E, Certificate of Exemption for Pass-through Withholding, to you. Individuals cannot claim the exemption from pass-through withholding by filing Form IL-1000-E. For tax years ending:

  • On or after December 31, 2014, you must include these amounts on your Form IL-1120-ST and Schedule B, Partners' or Shareholders' Information. You must also complete and retain a copy of Schedule K-1-P(3), Pass-through Withholding Calculation for Nonresident Members, for each of your nonresident shareholders.
    Note: If you are a fiscal-year filer and file during a year with a tax rate change, you will be required to complete Schedule K-1-P(3)-FY, Pass-through Withholding Calculation for Nonresident Members (for Fiscal Filers), instead. See the Schedule K-1-P(1) Instructions for more information.
  • Before December 31, 2014, you must file Form IL-1023-C, Composite Income and Replacement Tax Return, or Form IL-1000, Pass-through Entity Payment Income Tax Return.
    Note: Prior year forms and instructions for each tax type can be found by clicking the "Prior Years" link on our Business Tax Forms page and selecting the corresponding year.

See the IL-1120-ST Instructions for due dates and filing requirements.

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