What is the due date of Form IL-1120-ST?

In general, Form IL-1120-ST, Small Business Corporation Replacement Tax Return, is due on or before the 15th day of the 3rd month following the close of the taxable year. We grant you an automatic seven-month extension of time to file your small business corporate tax return. 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 file Schedule B, Partners' or Shareholders' Information, and your Form IL-1120-ST by the 15th day of the 3rd month following the close of the tax year. The automatic seven-month extension of time to file applies to this filing. An extension of time to file does not extend the amount of time to pay this liability.
  • Before December 31, 2014, you must file Form IL-1023-C, Composite Income and Replacement Tax Return, by the 15th day of the 4th month following the close of the tax year, or Form IL-1000, Pass-through Entity Payment Income Tax Return, by the 15th day of the 3rd month following the close of the tax year. The automatic seven-month extension of time to file applies to Form IL-1023-C filers, but does not apply to Form IL-1000 filers. An extension of time to file does not extend the amount of time to pay this liability.
    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.

Note: You are not required to file a form in order to obtain the automatic extension. However, if you expect tax to be due, you must use Form IL-1120-ST-V, Payment Voucher for Small Business Corporation Replacement Tax to pay any tentative tax due to avoid interest and penalty on tax not paid by the original due date of the return. An extension of time to file your Form IL-1120-ST does not extend the amount of time to pay your Illinois tax liability.

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