35 ILCS 200/16-85
The board of review in counties with less than 3,000,000 inhabitants, shall, on or before the annual date for adjournment as fixed by Section 16-35, complete its work and make the entries in the assessment books required to make the assessment conform to the changes made therein by the board of review, and shall attach to each book an affidavit signed by at least 2 members of the board, which affidavit shall be substantially in the following form: State of Illinois, County of ....,
We, and each of us, as a member of the board of review of the county of .... in the State of Illinois, do solemnly swear that the book to which this affidavit is attached contains a full and complete list of all the property in the county subject to taxation for the year .... so far as we have been able to ascertain, and that the assessed value set down opposite the description of a 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 columns in the book are correct, to the best of our knowledge and belief.
Dated ....
35 ILCS 200/16-85