Illinois law provides the Certificate of Error mechanism to allow the Cook County Assessor’s Office (“Assessor”) to apply two types of corrections to a prior year’s assessment. Certificate of Errors can be filed for the three prior tax years after the date on which the Cook County Treasurer’s Office (“Treasurer”) entered a judgment order for the annual tax sale.
What does “three prior tax years” mean?
If you are seeking a correction to your assessment for tax year 2021, the Treasurer entered a judgment order for that annual tax sale in 2023. Because tax year 2023 falls within the three years prior to the current year, 2025, the Assessor can correct the assessment for tax year 2021, presuming there was a mistake warranting correction. At this time, a Certificate of Error can be filed for tax years 2024, 2023, 2022, and 2021.
There are three types of Certificates of Error
- Assessed Value Corrections: To correct a property's assessed valuation in a year after the Assessor certified the property’s assessed value, typically after the Treasurer issues second installment tax bills. To learn more about filing a Certificate of Error please consult the Assessor’s Official Appeal Rules (Rule 27), at Official Appeal Rules of the Cook County Assessor | Cook County Assessor's Office.
- Corrections for Factual Errors: This includes property characteristic (e.g., # of bedrooms, baths, etc.) changes, class changes and building square footage corrections.
- Homestead Exemptions: File for missing homestead exemptions for past tax years. To learn about filing for past exemptions, visit, www.cookcountyassessor.com/certificates-error.
FREQUENTLY ASKED QUESTIONS
How and when do I apply
There are two ways to file a Certificate of Error.
- With a current year assessment appeal using our online SmartFile application during the applicable township filing window.
- As a standalone filing at any time during an assessment year by sending an email to Assessor.onlineappeals@cookcountyil.gov.
To learn more about filing a Certificate of Error please consult the Assessor’s Official Appeal Rules (Rule 27) at File an Appeal Online | Cook County Assessor's Office.
For township filing window dates, visit the Assessor’s Appeal Calendar at Assessment & Appeal Calendar | Cook County Assessor's Office.
* The Assessor strongly recommends that taxpayers file Certificates of Error with a current year appeal, as it is then easier for filers and our office to track the filings.
How does the approval process work?
Step 1. The Assessor assigns the filing of a Certificate of Error to a human analyst for review. The Assessor’s analyst reviews the Certificate of Error application along with all evidence the filer submitted in support of their request for a reduction in assessed value, a change in property characteristics and/or classification.
Step 2. The Assessor’s analyst reviews the filing to determine whether an error or mistake in the assessment warrants correction (a “change” or “no change”).
Step 3. If the Assessor’s analyst finds no error or mistake in the assessment to warrant correction, the Assessor will mail a letter to the filer denying the Certificate of Error.
Step 4. If the Assessor’s analyst finds an error or mistake in the assessment warranting correction, the Assessor will calculate a new recommended assessed value for the requested tax year(s), and issue the Certificate of Error.
Step 5. The Assessor must next identify whether the Certificate of Error it issued requires approval and endorsement by the Board of Review and/or adjudication by the Circuit Court. More information on these requirements is provided below.
Step 6. Once the above steps are complete, and if the Assessor granted a reduction in value, we mail a Certificate of Error recommended bill to the taxpayer (or their counsel) indicating the new estimated tax amount due. The Treasurer will validate the actual tax amount due.
Step 7. The Assessor certifies and transmits the adjusted Certificate of Error recommended bill information to the Treasurer to issue a refund.
How can I look up the status of my Certificate of Error filing?
The Certificate of Error Status Search, also known as the “Tracker”, is a quick way to find the status of certain types of Certificates of Error.
The following types of Certificates of Errors can be found using the Tracker:
• Valuation based, including those issued to activate property tax incentives or classification changes.
• Those based on Homestead exemptions.
• Those based on non-homestead exemptions.
Please note that Certificates of Errors which are submitted either by paper or via email will not appear on the Tracker until the Certificates of Error have been entered into the Assessor’s system of record.
The following types of Certificates of Errors cannot be found using the Tracker:
• Omitted Assessments
• Farmland-related Certificates of Error.
• Exempt-related Certificates of Error.
If you have questions, contact the Taxpayer Resolution Department at Assessor.Taxpayer.Resolution@cookcountyil.gov.
- How long does it take for a Certificate of Error application to be reviewed and processed?
The Assessor may only issue Certificates of Error it granted in accordance with the provisions of the Property Tax Code. 35 ILCS 200/14-15. No Certificates of Error the Assessor granted can be issued after the requested tax year is closed, even if a filer requested a Certificate of Error before the close of the tax year in question. The Assessor makes every effort to review all Certificate of Error requests in order of receipt and prior to the tax year closing deadline.
Generally, filers should expect the process of issuing and certifying Certificates of Error to take up to two (2) years, in some cases longer where statutorily required. This is true primarily for valuation based Certificates of Error. Homestead exemption based Certificates of Error can typically be issued and certified in a shorter period of time.
- I received an approval email and still haven’t received a refund check.
Currently, the Assessor does not send approval emails for valuation based Certificates of Error. The approval email is for a homestead exemption Certificate of Error. You may want to clarify with the Assessor’s “Taxpayer Services (TPI)” department.
- When does the Board of Review have to approve and endorse (or deny) certain Certificates of Error?
If you filed an assessment complaint at the Board of Review for the same tax year as any Certificate of Error that the Assessor later grants and issues, and which would reduce that Board of Review-certified assessment, the Assessor must submit that Certificate of Error to the Board of Review for further review, approval and endorsement before the Assessor can certify it. 35 ILCS 200/14-15.
- When does the Circuit Court have to adjudicate a Certificate of Error?
When the Assessor grants a reduction that would reduce the assessed value by $100,000 or more for a non-residential property (i.e., commercial or industrial), the Certificate of Error must be presented to the Circuit Court and filed as an objection to the annual tax sale for the tax year at issue. This means that if the Assessor made such a reduction in value via a Certificate of Error for the 2024 tax year, the Assessor cannot present the Certificate of Error to the Circuit Court until after the date of the annual sale for tax year 2024. That date would fall sometime in 2026 or 2027, depending upon when the Treasurer holds the annual tax sale. 35 ILCS 200/14-15.