35 ILCS 200/18-233
Adjustments for certificates of error, certain court orders, or final administrative decisions of the Property Tax Appeal Board. Beginning in levy year 2021, a taxing district levy shall be increased by a prior year adjustment whenever an assessment decrease due to the issuance of a certificate of error, a court order issued pursuant to an assessment valuation complaint under Section 23-15, or a final administrative decision of the Property Tax Appeal Board results in a refund from the taxing district of a portion of the property tax revenue distributed to the taxing district. On or before November 15 of each year, the county treasurer shall certify the aggregate refunds paid by a taxing district during such 12-month period for purposes of this Section. For purposes of the Property Tax Extension Limitation Law, the taxing district's most recent aggregate extension base shall not include the prior year adjustment authorized under this Section.
35 ILCS 200/18-233