The Illinois Department of Revenue is warning taxpayers that a change in how the U.S. Postal Service handles postmarks could affect mailed tax returns and payments in 2026. The department says the postmark will still show the date of first automated processing, not necessarily the day a piece of mail was dropped off at a local post office.
That matters because Illinois taxpayers face a Wednesday, April 15 filing deadline, and a delay in the recorded date could turn an on-time mailing into a late one. David Harris, the department’s spokesman, said taxpayers should not wait until the last day if they are mailing returns, and should request manual postmarks at the post office if they are sending a return near the deadline.
Harris said the department’s aim is to keep taxpayers from facing avoidable stress and penalties. He said the safest way to make sure the state receives a return or payment on time is to file electronically. Taxpayers can use tax.illinois.gov for free electronic filing and payment options, including MyTax Illinois, which allows returns and payments to be filed for free.
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The USPS guidance was published in the Federal Register at 90 Fed. Reg. 52883. Under the new approach, the postal mark may no longer match the exact moment a letter was handed over at a neighborhood branch, though manual local postmarks will still be available free of charge at retail locations upon request. That keeps a paper trail available for people who need it, but only if they ask for it.
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There is also a fallback for taxpayers who are not required by Illinois law to file or pay electronically. They may drop off returns or payments at an Illinois Department of Revenue office, where staff will date stamp the documents to provide proof of receipt. For everyone else, the department is making the same point in more direct terms: planning ahead is the best way to avoid late penalties, and in a year when the postmark may not mean what many filers assume, waiting until the last day is the riskiest move.
