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, click the "Prior Years" link on our Business Tax Forms page and select the corresponding year for information about the due date and what forms to file.

Note: You are not required to file a form 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.