Illinois warns USPS postmark changes could affect 2026 tax filing deadlines

CHICAGO - The Illinois Department of Revenue (IDOR) is alerting taxpayers that changes announced by the United States Postal Service (USPS) regarding postmarks could impact tax filings in 2026.

While the USPS postmark will still show the date of the first automated processing operation, the postmark may no longer reflect the date when the piece of mail was dropped off at a local post office. This change can directly impact time-sensitive documents such as tax returns and payments.

IDOR encourages those taxpayers who mail their returns and tax payments to do so earlier than they typically would to ensure they meet the Wednesday, April 15 filing deadline.

“Our goal is to help taxpayers avoid unnecessary stress and penalties, “explained IDOR Director David Harris. “If returns are mailed, taxpayers should not wait until the last day, or they should request manual postmarks at the post office if they are mailing a return near the filing deadline.”

USPS will continue to apply manual local postmarks upon request at retail locations free of charge. These manual postmarks will align with the date USPS first takes possession of the mail.

Harris stressed that electronic filing is the simplest and most convenient way to ensure tax documents and payments are received in a timely manner.

“The most reliable method to ensure IDOR receives a return or payment on time is to submit them electronically,” Harris said. “Taxpayers may visit tax.illinois.gov for free electronic tax filing and payment options and use MyTax Illinois to file a return and make payments for free.”

Taxpayers who are not required by Illinois law to file or pay electronically may drop off returns or payments at an IDOR office. IDOR staff will date stamp documents to provide accurate proof of receipt.

“Planning ahead is the best way taxpayers can protect themselves from late penalties,” Harris said. “Allowing extra mailing time, obtaining a manual postmark or IDOR date stamp, or using electronic filing options can reduce delays and ensure returns and payments are received 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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