35 ILCS 516/112
At any time before a judgment and order of sale is entered in any proceeding to collect or to enjoin the collection of taxes, the owner may file an affidavit with the board of review that the tax bill is in error as to the square footage or as to the rate of tax. The board of review, with the consent of the chief county assessment officer, may issue the person erroneously assessed a certificate of error setting forth the nature of the error and the cause or causes of the error. The certificate, when properly endorsed by a majority of the board of review and by the chief county assessment officer showing their concurrence, and not otherwise, may be used in evidence in any court of competent jurisdiction and, when introduced in evidence, shall become part of the court record and shall not be removed from the files except on an order of the court.
35 ILCS 516/112