The Illinois Department of Revenue is warning taxpayers that a change announced by the United States Postal Service to how postmarks are applied could affect timely filing and payment of 2026 tax returns. Under the new practice, the visible postmark on mailed items will reflect the date of the first automated processing operation rather than necessarily showing the date the piece of mail was dropped off at a local post office — a shift that could make last‑minute mailed returns appear late.
IDOR officials say the difference between a local drop‑off time and the automated processing date can be significant for documents tied to strict deadlines, such as the Wednesday, April 15 filing date. The department is urging anyone who plans to mail returns or payments to allow extra mailing time this filing season and to consider alternatives that eliminate reliance on a processing‑date postmark.
IDOR Director David Harris highlighted options taxpayers can use to protect themselves from penalties. “Our goal is to help taxpayers avoid unnecessary stress and penalties,” Harris said. “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.” The USPS has said retail locations will continue to apply manual local postmarks at customers’ request, free of charge; those manual marks will reflect the date the Postal Service first takes possession of the mailpiece.
Electronic filing remains the department’s preferred safeguard against late‑filing issues. Harris pointed taxpayers to free online tools: “The most reliable method to ensure IDOR receives a return or payment on time is to submit them electronically,” he said, noting taxpayers may visit tax.illinois.gov for e‑filing and payment options and can use MyTax Illinois to file returns and make payments at no cost.
For taxpayers who cannot or prefer not to file electronically, IDOR offices will accept hand‑delivered returns and payments and will apply a date stamp to provide official proof of receipt. The department reiterated that planning ahead — mailing earlier, obtaining a manual postmark, or using an IDOR date stamp — can reduce the risk of delays and late‑filing penalties.
The USPS published its guidance in the Federal Register (90 Fed. Reg. 52883), and IDOR advised taxpayers to check applicable return instructions and the Tax Forms Index for specific due dates and additional filing details. With the postmark practice change taking effect this year, state revenue officials caution that relying on last‑minute postal drop‑offs without requesting a manual stamp could leave filers exposed to avoidable penalties.