Illinois Tax Filings Affected by USPS Postmark Changes

IL DOR Informational Bulletins

Published January 1st, 2026

Detected March 13th, 2026

Summary

The Illinois Department of Revenue (IDOR) issued a notice regarding changes to United States Postal Service (USPS) postmarks that could impact the timely filing of Illinois tax returns and payments in 2026. Taxpayers are advised to file and pay electronically or mail returns earlier to avoid late penalties.

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What changed

The Illinois Department of Revenue (IDOR) has issued a notice informing taxpayers and tax professionals about changes to United States Postal Service (USPS) postmarks that may affect the timely filing of Illinois tax returns and payments starting in 2026. The USPS postmark may no longer accurately reflect the date mail was dropped off, potentially impacting time-sensitive documents like tax filings. This notice references a USPS guidance document published in the Federal Register (90 Fed. Reg. 52883).

To mitigate the risk of late filing or payment penalties, IDOR strongly recommends taxpayers file and pay electronically via MyTax Illinois or tax.illinois.gov. For those who choose to mail their returns and payments, IDOR advises mailing them earlier than usual. Taxpayers can also request manual postmarks at USPS offices, which are assured to reflect the date USPS takes possession of the mail, or drop off documents in person at an IDOR office for official date stamping.

What to do next

Advise clients and internal teams of potential delays in USPS postmark dates.
Prioritize electronic filing and payment for all Illinois tax obligations.
If mailing is necessary, ensure tax documents and payments are sent significantly earlier than usual to account for potential postmark discrepancies.

Penalties

Late filing or late payment penalties may apply if returns and payments are not received by IDOR on time.

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Scam Alert: Fake Texts and Websites Impersonating IDOR

Be alert for fraudulent messages or websites attempting to steal your banking information, login credentials, or credit card details. The Illinois Department of Revenue (IDOR) will never request personal or financial information via text message. To confirm official communications or contact details, always visit https://tax.illinois.gov.

Employment Sign Up for Updates

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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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:

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.
- Visit tax.illinois.gov for free electronic tax filing and payment options.
- Use MyTax Illinois to file and pay your return or payment for free.
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.