Illinois Department of Revenue Reminds Taxpayers of Postal Service Changes That May Affect Tax Filing Deadlines

SPRINGFIELD – The Illinois Department of Revenue (IDOR) is reminding taxpayers about changes announced by the United States Postal Service (USPS) regarding postmarks that could affect tax filing deadlines in 2026.

Under the updated USPS procedures, postmarks will continue to reflect the date of the first automated processing operation, however, they may no longer indicate the date a piece of mail was dropped off at a local post office. This distinction may impact time-sensitive materials, including tax returns and payments.

IDOR encourages taxpayers who plan to mail their returns or payments to send them earlier than usual to help ensure they meet the Wednesday, April 15 filing deadline.

“We are reminding taxpayers of this change so they can plan accordingly and avoid potential delays,” said IDOR Director David Harris. “If you’re mailing your return close to the deadline, consider requesting a manual postmark or allowing extra time for delivery.”

USPS will continue to provide manual postmarks at retail locations upon request at no cost. These postmarks reflect the date the postal service takes possession of the mail. Taxpayers who are not required to file or pay electronically may also choose to deliver returns or payments in person at an IDOR office, where documents will be date-stamped as proof of receipt.

Harris stressed that electronic filing remains the simplest and most efficient option for meeting the April 15 deadline.

“Filing electronically is still the easiest way to make sure your return or payment is submitted on time,” Harris said. “Taxpayers can visit tax.illinois.gov to explore free filing and payment options and use MyTax Illinois to file a return and make payments for free.

“Planning ahead now can help prevent issues later,” Harris said. “Mailing early, requesting a manual USPS postmark or IDOR date stamp, or filing electronically can help ensure everything is submitted on time.”

For more information on this change, visit the USPS’s guidance published in the Federal Register (90 Fed. Reg. 52883). See the applicable return instructions to confirm due dates for returns and payments. These instructions are available in the Tax Forms Index.

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