65 ILCS 5/3.1-50-5

All municipal officers, except as otherwise provided, shall receive the salary or other compensation that is fixed by ordinance. Salaries or other compensation shall not be increased or diminished so as to take effect during the term of any officer holding an elective office. The salaries, fees, or other compensation of any appointed municipal officer, not including those appointed to fill vacancies in elective offices, may be increased but not diminished so as to take effect during the term for which the officer was appointed.