35 ILCS 200/16-150
In counties with 3,000,000 or more inhabitants, the board of appeals (until the first Monday in December 1998 and the board of review beginning the first Monday in December 1998 and thereafter) shall, on or before the annual date for final adjournment as fixed by this Section, complete its work, and order the county assessor to make those entries in the assessment books and lists as may be required to make the assessments conform with the changes directed to be made therein by the board. The county assessor and a majority of the members of the board shall attach to each of the assessment books in the possession of the county assessor and the county clerk an affidavit signed by the county assessor and a majority of the members of the board, which affidavit shall be in substantially the following form:
State of Illinois)) ss. County of .......) We, and each of us, as county assessor and as members of the (board of appeals or board of review) of the County of ...., in the State of Illinois, do solemnly swear that the books .... in number .... to which this affidavit is attached, contain a full and complete list of all the property in this county subject to taxation for the year (insert year) so far as we have been able to ascertain them, and that the assessed value set down in the proper column opposite the several kinds and descriptions of property, is, in our opinion, a just and equal assessment of the property for the purposes of taxation according to law, and that the footings of the several columns in these books are correct to the best of our knowledge and belief.
The final date of adjournment of the board shall be 60 days after the date of the last delivery to it of the assessment books for any township or taxing district.
35 ILCS 200/16-150