65 ILCS 5/4-5-22
In addition to the duties now imposed by law upon a municipal treasurer, the treasurer of a municipality under the commission form of municipal government shall deposit all money the treasurer receives from all sources of revenue, to his or her credit as treasurer of the municipality, in one or more places of deposit designated in the same manner and subject to the same conditions as provided in Section 3.1-35-50.
The treasurer (i) shall collect any interest paid on these deposits, (ii) shall report that interest in the treasurer's next statement following its collection, and (iii) shall credit the interest to the particular fund of the municipality upon which the interest accrued. This interest shall be treated as a part of that particular fund and shall be subject to use for any purpose for which the fund may be used.
65 ILCS 5/4-5-22