35 ILCS 200/9-245
In counties with less than 3,000,000 inhabitants, the chief county assessment officer shall on or before the third Monday in June of the assessment year, or on or before the 90th day following the certification of the final township assessment roll in the county, certified pursuant to Section 9-230 of this Code, whichever is later, return the assessment books to the board of review verified by affidavit, substantially in the following form: State of Illinois)
) ss.
........... County)
I,...., chief county assessment officer do solemnly swear that this book contains a correct and full list of all the property subject to taxation in...., so far as I have been able to ascertain the same; and that the assessed value set down in the column opposite the descriptions of property is a just and equitable assessment under the law, to the best of my knowledge and belief, and that the footings of the columns and the accompanying tabular statement, are correct to the best of my knowledge and belief.
Dated..........
35 ILCS 200/9-245