The sheriff's office merit commission in counties having a population of four hundred thousand inhabitants or more as determined by the most recent federal decennial census shall consist of five members. One member shall be a duly elected county official, appointed by the county board. One member shall be a deputy sheriff, elected by the deputy sheriffs. Three members shall be selected by the presiding judge of the judicial district encompassing such county and shall be public representatives who are residents of the county. The terms of office of members initially appointed or elected shall expire on January 1 of the first, second, and third years following their appointment or election, as designated by the county board. As the terms of initial members expire, their successors shall be appointed or elected for three-year terms in the same manner as the initial members. The additional public representative provided for in this section shall serve until January 1, 1984, and thereafter his or her successors shall be appointed or elected for three-year terms. Any vacancy shall be filled by appointment or election in the same manner as appointment or election of initial members. The commission shall have the power to declare vacant the position of any member who no longer meets the qualifications for election or appointment set out in this section.