40 ILCS 5/5-180
A vacancy on the board owing to death, resignation or any other cause shall be filled as follows: If the vacancy is of an appointee of the mayor, the mayor shall appoint a person to serve for the remainder of the unexpired term. If the vacancy is of an active policeman member, or a pensioner or annuitant member, the successor shall be elected to serve during the remainder of the unexpired term, at a special election which shall be held by the board within 30 days from the date the vacancy occurs. The election shall be conducted in the same manner as the regular triennial election herein provided for.
The appointive members of the board may be removed from office by the mayor. Any member elected by the active policemen who withdraws from the police service of the city shall automatically cease to be a member of the board.
Any elective member of the board shall be subject to recall as follows: If not less than 60% of the active policemen contributors to the fund, or not less than 60% of the pensioners and annuitants (minors under age 18 excepted), petition the board in writing to declare vacant the membership of an active policeman member or pensioner or annuitant, as the case may be, respectively, the board, within 15 days after receipt of the petition shall declare such membership vacant. A member of the board is not subject to recall more than once in any calendar year nor within one year after a previous recall.
40 ILCS 5/5-180