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 corporation), 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 federal Form 1120S, U.S. Income Tax Return for an S Corporation (regardless of net income or loss).   

See our Subchapter S (Small Business) Corporation web page for more information.                                                                                                                                                    

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