Mo. Rev. Stat. § 98.030

All cities and towns having a population of less than ten thousand and acting under special charters, may, by ordinance, provide for the election of police judges in such cities, who shall be elected at the municipal election, and shall, when so elected, have exclusive jurisdiction to hear and determine all offenses against the ordinances of such cities; provided, that when such police judge shall be elected, then the jurisdiction conferred on the mayor to hear and determine cases for the violation of city ordinances by the charter of such city shall be held to refer to the police judge elected under this section.