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Informational
Bulletin

FY 2026-17
January 2026

David Harris, Director

This bulletin is written to inform you of recent changes; it does not replace statutes, rules and regulations, or court decisions.

For more information visit: tax.illinois.gov

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Printable version available in:
English

FY 2026-17, Changes to United States Postal Service on Postmarks Could Impact Illinois Tax Filings

To: All taxpayers and tax professionals filing Illinois tax returns and paying Illinois taxes

The United States Postal Service (USPS) has announced changes to postmarks that 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.

What steps can I take to file and pay my Illinois taxes timely?

Taxpayers are responsible for ensuring timely filing and payment. Here’s how to avoid late penalties:

1. File and pay electronically

  • The most reliable method to ensure that Illinois Department of Revenue (IDOR) receives a return or payment on time is to submit them electronically.

2. Drop off in person

  • Taxpayers who are not mandated under Illinois law to file or pay electronically may drop off a return or payment at an IDOR office. IDOR personnel will date stamp your documents to ensure accurate records.

If I choose to continue mailing my tax forms and payments to IDOR, what can I do to mitigate the possibility of getting a late filing or late payment penalty?

USPS will continue to add manual postmarks upon request at their offices. This USPS’s guidance assures the public that these manual postmarks will align with the date that USPS first takes possession of the mail. IDOR encourages taxpayers who mail their returns and tax payments to mail those items earlier than they typically would to ensure timely delivery.

Where can I find additional information?

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 your returns and payments. These instructions are available in the Tax Forms Index.

Printed by authority of the State of Illinois — Electronic only, One copy