Certificates of Error
Illinois law provides the Certificate of Error procedure to allow the Cook County Assessor to apply changes to a property tax bill that has already been issued. 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.
Missing Property Tax Exemptions? Homeowners can apply for Certificates of Error(s).
If your home was eligible for a homestead exemption in a prior tax year (2017, 2018, 2019, 2020) but the exemption was not applied to the property tax bill, 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. For Tax Year 2020, the Certificate of Error filing will result in a corrected bill or a refund, depending on the time of the filing.
The Assessor’s Office is pleased to bring this process online for the first time.
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 the missed exemption. For example, to apply for a Homeowner Exemption Certificate of Error for Tax Year 2019, 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, 2019.
Please review the steps below to apply. Our staff are ready to assist you so that your application is submitted successfully.
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Certificate of Error applications requesting homestead exemptions for tax years 2017, 2018, 2019, and 2020 are available.
- Homeowner Exemption: Apply Online | Form
- Senior Exemption: Apply Online | Form
- Senior Freeze:
- Persons with Disabilities: Apply Online | Form
- Returning Veterans: Apply Online | Form
- Veterans with Disabilities: Apply Online | Form
Common Supplemental/Related Forms for Exemptions
- PTAX 343-A
- Occupancy Affidavit (note: to assist taxpayers, all exemption Certificate of Error applications automatically include this Occupancy Affidavit, and the CCAO has waived the notarization requirement.)
- Homeowner Exemption Waiver
- Affidavit of Person Claiming Senior Citizens Assessment Freeze Homestead Exemption Due to a Deceased Taxpayer
Forms: Certificates of Error for Property Assessed Valuations
- Taxable Property Certificate of Error
- Tax-Exempt Property Certificate of Error
- Omitted Assessment Certificate of Error
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.
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