35 ILCS 200/5-10
Each member of the board of review or commissioner of the board of appeals created by this Code shall, before entering upon the duties of his or her office, take and subscribe to the following oath: State of Illinois County of ....
I do solemnly swear (or affirm) that I will as (a member of the board of review) (a commissioner of the board of appeals) faithfully perform all the duties of that office as required by law; that I will fairly and impartially review the assessments of all property to the extent authorized by this Code; that I will correct all assessments which should be corrected; that I will raise or lower (or in the case of commissioners of the board of appeals, will direct the county assessor to change, correct, alter or modify) assessments as justice may require; and that I will do all acts necessary and within my authority to procure a full, fair and impartial assessment of all property.
Dated ....
35 ILCS 200/5-10