Illinois I Business State Tax Extension I S Corporations

Modified on Tue, 21 Jan at 3:54 PM

State NameIllinois
Business Entity TypeS-Corporations
Extension StatusApproved with Federal
Return Due DateMarch 15, 2025
Extended Due DateSeptember 15, 2025
Other Information
  • Illinois grants your business an automatic 6-month extension provided you have obtained an approved IRS extension.
  • The extension is NOT an extension to pay any taxes you may have due.
  • Tax payments are due by the original return due date.
Online PaymentIllinois | Online Tax Extension Payment
Payment Voucher FormIL-1120-V | Payment Voucher for Corporation Income and Replacement Tax
State Payment AgencyIllinois Department of Revenue
Mailing Address with Payment

Illinois Department of Revenue
P.O. Box 19038
Springfield, IL 62794-9038

Failure to File Penalties

Late filing:

  • Lesser of $250 or 2% of tax liability, reduced by timely payments or credits.

Nonfiling:

  • Greater of $250 or 2% of tax liability up to $5,000, if a return is not filed within 30 days after receiving a notice of nonfiling.
Failure to Pay Penalties

Before audit:

  • 2% of tax liability for payments 1-30 days late.
  • 10% of tax liability for payments 31 or more days late.

After audit initiation:

  • 15% of tax liability if paid within 30 days after issuance of the audit-prepared amended return or waiver of restrictions on assessment.
  • 20% of tax liability if taxpayer:
  • paid after the expiration of the 30-day period;
  • paid under protest; or
  • claims a credit or refund for tax, penalties, or interest determined due upon audit.

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