65 ILCS 5/11-46-3
The 3 members of the commission required to be appointed from among the professions enumerated in Section 11-46-2 shall be appointed in the first instance for one, 2, and 3 year terms of office respectively, as the mayor may determine. The other appointed members of the commission also shall be appointed in the first instance for one, 2 and 3 year terms of office respectively. After the expiration of these first terms of office of all of the appointed members respectively, their successors shall be appointed for a term of 3 years in each case. All appointments to fill vacancies shall be for the unexpired term.
In case a vacancy occurs in the commission for any reason the vacancy shall be filled by appointment by the mayor. All appointees shall hold their offices for their respective terms and until their successors are appointed and have qualified.
65 ILCS 5/11-46-3