Who must file the IL-1120-ST?

Who must file the IL-1120-ST?

You must file Form IL-1120-ST, Illinois Small Business Corporation Replacement Tax Return, if you are a small business 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 U.S. Form 1120S (regardless of net income or loss).
  

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