65 ILCS 5/8-2-9.1
Every municipality with a population of less than 500,000 (except special charter municipalities having a population in excess of 50,000) that has adopted this Section 8-2-9.1 and Sections 8-2-9.2 through 8-2-9.10 by a two-thirds majority vote of those members of the corporate authorities then holding office shall have a budget officer who shall be designated by the mayor or president, with the approval of the corporate authorities. In municipalities operating under the commission form of government, the commissioner of accounts and finances shall designate the budget officer, with the approval of the council or board of trustees, as the case may be. In municipalities with a managerial form of government, the municipal manager shall designate the budget officer. The budget officer shall take an oath and post a bond as provided in Section 3.1-10-25. The budget officer may hold another municipal office, either elected or appointed (including, but not limited to, the office of mayor or president in municipalities with a population under 10,000), and may receive compensation for both offices except when a mayor or president in a municipality with a population under 10,000 is also the budget officer. Article 10 of this Code shall not apply to an individual serving as the budget officer. The budget officer shall serve at the pleasure of the mayor or municipal manager, as the case may be.
65 ILCS 5/8-2-9.1