Certificates of Error

Illinois law provides the Certificate of Error procedure to allow the Cook County Assessor to apply changes to a tax year in the past (i.e., for Tax Year 2018 or before). It is a way to correct a tax bill after the assessment for that tax year is finalized. 

One Certificate of Error application addresses a single tax year. If you are entitled to a value reduction for more than one year, a Certificate of Error request must be filed for each individual year. Note that Certificate of Error applications can be denied. You can review the Reason Codes for a denial of a Certificate of Error application. 


Forms: Certificates of Error for Exemptions

If you and your property were eligible for an exemption for your home in a prior tax year but did not receive the exemption, these forms can be used to apply for Certificates of Error for Tax Year 2018 or before.

The property must have been eligible in that tax year and the applicant must provide supporting documentation to demonstrate eligibility. For example, to apply for a Homeowner Exemption Certificate of Error for Tax Year 2018, you must demonstrate property tax liability and residency as of January 1, 2018. If you have questions, please contact us. 

To apply for exemptions for tax year 2019 (billed in 2020), please visit our Exemptions page.


Forms: Certificates of Error for Property Assessed Valuations


Common Supplemental/Related Forms for Exemptions


What happens after I submit a Certificate of Error application?

After a Certificate of Error application is received, it must be processed through the Assessor’s Office. If the property’s assessment has been previously reviewed by the Board of Review, the Board of Review must approve the Certificate of Error as well. In addition, Certificate of Error applications for non-residential properties that seek a reduction of more than $100,000 in assessed value must be sent to the Circuit Court for a judge’s consideration.

If a Certificate of Error does not have to go to court for review, you will receive a letter from the Assessor’s Office which indicates whether the Certificate of Error has been granted or denied.

Certificate of Error applications can be denied. You can review the Certificate of Error Denial Reason Codes.

If the Certificate of Error is required to go to court for adjudication, a letter regarding the outcome of that Certificate of Error request will be sent to you by the Cook County State's Attorney’s Office.