35 ILCS 200/20-220
Within 15 days after the receipt of a request by a taxing district, the collector shall issue a certificate (hereinafter referred to as the "Certificate") to the governing body or corporate authorities of the taxing district setting forth (i) the aggregate amount of all taxes collected on extensions upon pollution control facilities, as defined in Section 11-10, by and distributed to the taxing district prior to the date of the issuance of the Certificate, if those taxes have been held illegal by the final order of a court, or any board, body or entity having jurisdiction, because the pollution control facilities within the taxing district were incorrectly assessed or valued, based upon the method of valuation under Section 11-15, at the time taxes levied by or on behalf of the taxing district were extended (hereinafter referred to as the "illegal taxes"), (ii) the aggregate amount of the illegal taxes required to be deducted from the taxes of the taxing district during the same calendar year as, and during the 2 full calendar years immediately following, the date of the issuance of the Certificate (hereinafter referred to as the "taxes to be deducted"), and (iii) the aggregate amount of the illegal taxes deducted during the same calendar year as, and during the 2 full calendar years immediately preceding, the date of the issuance of the Certificate (hereinafter referred to as the "deducted taxes").
35 ILCS 200/20-220