Certificates of Error

Illinois law provides the Certificate of Error procedure to allow the Cook County Assessor to apply changes to a prior tax year (i.e., for Tax Year 2018 or before). It is a way to make a correction 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 Certificate of Error for more than one year, a request must be filed for each individual year. Please note that Certificate of Error applications can be denied.

Certificates of Error for Exemptions

What is a Certificate of Error?

The deadline to apply for exemptions has passed, however homeowners can apply for Certificates of Error for tax years 2016, 2017 & 2018. For more information and details, watch this short video or click link below. www.cookcountyassessor.com/certificates-error

Posted by Cook County Assessor's Office on Wednesday, May 20, 2020


If your home was eligible for a homestead exemption in a prior tax year (2016, 2017, or 2018) and you already paid the full tax amount billed for that year, the Assessor’s Office can help you obtain a refund through the Certificate of Error process.

Applying for a Certificate of Error for an exemption is very similar to applying for an exemption. The Assessor’s Office is pleased to bring this process online for the first time. Tax Year 2019 applications will be accepted later this year after second installment property tax bills are sent.

The property must have been eligible in that particular tax year and you must provide a photo ID and any other required supporting documentation to demonstrate eligibility. For example, to apply for a Homeowner Exemption Certificate of Error for Tax Year 2018, you must provide at least one document from the list of accepted documents that demonstrate the home was your primary place of residence as of January 1, 2018.

Please review the steps below to apply. Our staff are ready to assist you so that your application is submitted successfully. 

Step 1:

Preview the Form carefully and prepare documents to show eligibility in that Tax Year. All applications require at least a photo ID and PIN

Step 2:

Contact us or your township assessor with any questions you have about the form or documents.

Step 3:

Apply online! An email address is required so that you can track your application.

Certificate of Error applications requesting homestead exemptions for Tax Years 2016, 2017, and 2018 are available:

 Common Supplemental/Related Forms for Exemptions

Forms: Certificates of Error for Property Assessed Valuations

Online filing is available if the Certificate of Error application is being submitted with a current year appeal.

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.