What is the due date of Form IL-1120?

For tax years beginning on or after January 1, 2016:

  • Original due date:

    Determine the date your tax year ends. If your tax year ends on:

    • a date other than June 30, Form IL-1120 is due on or before the 15th day of the 4th month following the close of the tax year.
    • June 30, Form IL-1120 is due on or before the 15th day of the 3rd month following the close of the tax year.

    Note: If you are a cooperative, Form IL-1120 is due on the 15th day of the 9th month following the close of the tax year regardless of when your tax year ends.

  • Automatic filing extension:

    Determine the date your tax year ends. If your tax year ends on:

    • a date other than June 30, we grant you an automatic extension of time to file your annual return of six months.
    • June 30, we grant you an automatic extension of time to file your annual return of seven months.

    Note: If you are a cooperative, we grant you an automatic extension of time to file your annual return of seven month regardless of when your tax year ends.

For tax years beginning before January 1, 2016, see the instructions which correspond to the year of the return you are filing. 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-V, Payment Voucher for Corporation Income and 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 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.