Fix a property record error: the Cook County Certificate of Error
A Certificate of Error in Cook County lets the Assessor correct a tax bill that was already issued, for a missing exemption or an assessed value. Factual errors in the Assessor's record, such as square footage, building details or class, can be reported at any time. Our $19 Record Correction Guide lists the differences and the proof; you submit it.
- Valuation Certificates of Error
- Most can be filed for tax years 2025, 2024, 2023 and 2022
- Missing homestead exemption
- Refund route for tax years 2021–2025
- How long it takes
- Valuation: up to two years. Exemption: usually faster
- Our guide
- $19, on its own or with Core or Full Season
Sources: Cook County Assessor's Office (Certificates of Error; 2026 Appeal Rules) · Last checked Oct 4, 2026
Record correction
- Differences between what you report and the county record (characteristics, class, exemptions)
- Guide to your county's record-correction route, with official sources
- Checklist of proof to include
- Price, one-time
- $19
What is a Certificate of Error in Cook County?
A Certificate of Error lets the Cook County Assessor correct a tax bill that was already issued, either for a missing exemption or for an assessed value. If the Board of Review already reviewed the assessment, the Board must also approve the Certificate of Error.
Which tax years can I correct?
- Valuation: most valuation Certificates of Error can currently be filed for tax years 2025, 2024, 2023 and 2022.
- Missing exemption: if an eligible homestead exemption was missing from a paid bill for tax years 2021–2025, you can apply for a refund through a Certificate of Error, online or by mail.
How do I file a Cook County Certificate of Error?
- For a valuation, file it with a current-year appeal in SmartFile, which the Assessor recommends, or on its own at any time by e-mail to the Assessor.
- For a missing homestead exemption, apply online or by mail.
- Include every document the first time. A valuation Certificate of Error needs the application and the same supporting documents as a current-year appeal, missing documents can lead to denial, and the Assessor does not re-review its decisions.
- For an exemption, include a photo ID and documents showing you were eligible in the tax year you apply for.
How long does a Certificate of Error take?
The Assessor says valuation Certificates of Error can take up to two years to complete; exemption ones are usually faster. For a missing Homeowner Exemption, the Assessor's FAQ says the Treasurer's refund follows the Certificate of Error in about 6 to 8 weeks.
What if my square footage or class is wrong?
Report factual errors in the Assessor's record, such as square footage, building characteristics, class or data-entry errors, at any time: through the Contact Us page, by e-mail, by mail, in person, or in SmartFile with an appeal. Send documents such as a plat of survey or photos.
The Assessor measures building square footage around the home's exterior, not room by room. Compare like with like before you report a difference.
Many characteristic corrections do not change the assessed value, the Assessor notes.
What if I have an exemption I no longer qualify for?
An owner who is no longer eligible for a homestead exemption can apply to the Assessor to remove it.
Can I file a Certificate of Error and a PTAB appeal for the same year?
Generally not. The Assessor's rules say state law generally bars filing both a Certificate of Error and a Property Tax Appeal Board or Circuit Court appeal for the same tax year. Not legal advice.
How are property record errors handled outside Cook County?
- Philadelphia: a Board of Revision of Taxes appeal can show that the recorded characteristics of the property are substantially incorrect.
- Providence: you can appeal to the Tax Assessor if the assessment is more than market value for any reason, including clerical errors, or if the class is wrong.
In these places the fix runs through the appeal itself, so its deadline applies. The guide covers only places whose correction rules we have checked.
What counts as a record error?
The county decides whether its record is wrong.
Home details
The county's record of your home's size or features, such as its square footage, doesn't match the home.
Property class
The class on the county's record looks wrong for your home.
Exemptions
An exemption you qualify for is missing from the record.
What's in the $19 Record Correction Guide?
Buy it on its own or add it to Core or Full Season; you don't need an appeal. You submit the request yourself, and the county decides whether to correct its record. We never file or contact the county for you.
Check your record free
The free check shows your county's record of your home, so you can spot a wrong detail before you buy anything.
Get the Record Correction Guide
Add to Core or Full Season, or buy on its own. No appeal needed.
You submit the request; the county decides
You gather the proof and submit the request to the county yourself. The county decides whether to correct its record.
Common questions
Will a correction lower my tax bill?
Do I need to appeal to fix a record error?
Is Property Appeal part of the Assessor's office?
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The free check shows your county's record of your home, so you can spot a wrong detail before you buy anything.
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