What is a Certificate of Error and how can I apply?

A Certificate of Error (COE) is a correction issued by the Cook County Assessor or the Cook County Board of Review when a property tax assessment contains a verified mistake.

If an error caused your property to be assessed incorrectly, a Certificate of Error may allow the county to correct the assessment and refund any overpaid property taxes.

This process is commonly used when mistakes are discovered after the normal property tax appeal deadlines have passed.

When Is a Certificate of Error Used?

A Certificate of Error is typically used when there is a clear factual error in the property record.

Common examples include:

• Incorrect building size or square footage

• Property classified incorrectly (such as residential vs. commercial)

• A building listed that does not exist

• Demolished structures still included in the assessment

• Incorrect number of units or property characteristics

The error must be documented and verifiable.

How Far Back Can a Certificate of Error Apply?

In Cook County, a Certificate of Error can usually be filed for up to three prior tax years if the error affected previous assessments.

If the correction is approved, the county may:

• Adjust the property assessment

• Issue a refund for overpaid property taxes

Who Can Apply for a Certificate of Error?

Applications can be submitted by:

• Homeowners

• Commercial property owners

• Attorneys or tax representatives

• Property managers acting on behalf of the owner

The property owner must provide documentation showing that the assessment error occurred.

How to Apply for a Certificate of Error

Step 1: Identify the Error

Review your property record carefully and confirm that a mistake exists in the county’s property information.

Examples include incorrect property details or classification errors.

Step 2: Gather Supporting Documentation

You may need documents such as:

• Property surveys

• Building plans

• Photographs

• Demolition permits

• Property records or legal documents

These help confirm that the assessment information is incorrect.

Step 3: Submit the Application

You can apply for a Certificate of Error through:

• The Cook County Assessor’s Office, or

• The Cook County Board of Review

Applications are usually submitted through the agency’s online portal or by filing the required forms.

Step 4: Wait for Review and Approval

The county will review your request and supporting evidence.

If the error is confirmed:

• A correction is issued

• The tax bill may be adjusted

• A refund may be processed for overpaid taxes

Important Difference Between an Appeal and a Certificate of Error

A property tax appeal challenges the value of your property during the appeal window.

A Certificate of Error corrects a factual mistake in the property record, often after appeal deadlines have passed.

Key Takeaways

• A Certificate of Error corrects mistakes in property tax assessments.

• It can apply to the current year and up to three prior tax years.

• Property owners must provide documentation proving the error.

• Approved corrections may result in a tax refund.

• Both homeowners and commercial property owners in Cook County can apply.

If you discover a factual error in your property record, applying for a Certificate of Error may help correct the assessment and recover overpaid property taxes.