The United States Postal Service (USPS) has announced a change in how postmarks are applied to mail, which could affect tax filings in Illinois for the 2026 tax year. According to the announcement, USPS postmarks will continue to display the date of the first automated processing operation. However, they may no longer indicate the date when mail was dropped off at a local post office.
This adjustment could have consequences for documents that are time-sensitive, such as tax returns and payments. The date shown on a postmark is often used to determine whether these documents were mailed on time.
Additional details about this change can be found in Informational Bulletin FY 2026-17, Changes to United States Postal Service on Postmarks Could Impact Illinois Tax Filings.