35 ILCS 200/16-75
The board of review shall, at any time before judgment, if an error or mistake is discovered (other than errors of judgment as to the valuation), in any assessment, issue to the person erroneously assessed a certificate setting forth the nature of the error and its cause or causes. The certificate when properly endorsed by the chief county assessment officer, showing concurrence therein, and not otherwise, may be used in evidence in any court of competent jurisdiction, and when so introduced in evidence, shall become a part of the court records, and shall not be removed from the files except upon the order of the court.
After the board of review has issued a certificate of error and it has been properly endorsed by the chief county assessment officer, 2 copies of the certificate shall be made and one copy given to the county clerk and one copy to the collector. The county clerk shall keep records of the changes or corrections made in the certificate and shall certify such corrections to the collector so that he or she can account for the proper amount of taxes chargeable to him or her.
35 ILCS 200/16-75