A Real Estate Certificate of Error (C of E) allows the Cook County Assessor to change a property’s assessed value for a prior year. Illinois law provides this procedure as a way to correct a tax bill after the assessment for that tax year is finalized. A Certificate of Error addresses a single 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.

After a C of E 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 C of E as well. In addition, non-residential C of E requests 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. If the C of E is required to go to court for adjudication, a letter regarding the outcome of that C of E request will be sent to you by the Cook County State's Attorney’s Office.

Certificate of Error application formsare available on the forms page of the Assessor’s Web site or by calling (312)443-7550.