Illinois Department of Revenue Warns Postal Changes Could Affect Tax Filing Deadlines

SPRINGFIELD — The Illinois Department of Revenue is warning taxpayers that changes by the United States Postal Service could affect tax filings in 2026. The agency said USPS postmarks will show the date of the first automated mail processing instead of the date a letter is dropped off at a local post office. Officials said this could affect time sensitive documents such as tax returns and payments. Taxpayers who plan to mail returns are encouraged to send them earlier to meet the April 15 filing deadline. USPS will still provide manual local postmarks at retail locations at no cost when requested. State officials said those postmarks will reflect the date the postal service takes possession of the mail. The department said electronic filing remains the most reliable way to ensure returns and payments are received on time. Taxpayers who are not required to file electronically may also drop off returns or payments at a Department of Revenue office where staff will date stamp the documents as proof of receipt.