65 ILCS 5/3.1-50-10
The corporate authorities of a municipality may fix the salaries of all municipal officers and employees in the annual appropriation or budget ordinance. They may fix the salary of all officers who hold elective office for a definite term in an ordinance other than the appropriation or budget ordinance. The salaries that are fixed in the annual appropriation ordinance shall neither be increased nor diminished during the fiscal year for which the appropriation is made. The salaries that are fixed by ordinance for those officers who hold elective office for a definite term shall neither be increased nor diminished during that term and shall be fixed at least 180 days before the beginning of the terms of the officers whose compensation is to be fixed.
65 ILCS 5/3.1-50-10