Mo. Rev. Stat. § 100.330
Subsequent to August 13, 1980, the number of commissioners shall be fifteen. Provided, however, by the process of attrition the number of commissioners shall be reduced from twenty-five to fifteen by the expiration of the terms of currently serving commissioners and nonreplacement of any vacancies. Commissioners shall be appointed for a term of four years each. All commissioners shall be appointed by the mayor or chief executive officer of the city, shall be taxpayers of the city, and shall have resided in the city for five years immediately prior to their appointment. All vacancies shall be filled by the mayor or chief executive officer of the city for the unexpired term, subsequent to the time the number of commissioners is reduced to fifteen by attrition.
§ 100.330, RSMo