Mo. Rev. Stat. § 78.080
In every city having a population of over three thousand and under eight thousand there shall be elected at the first municipal election held after the taking effect of this section, and every four years thereafter, a mayor and two councilmen, except in any city with a population of at least five thousand within a third class county which adjoins three other third class counties and one second class county and the state of Arkansas, wherein the law applicable before August 28, 1991, shall continue to apply; and in cities having a population of over eight thousand and less than thirty thousand, a mayor and four councilmen. For cities with a population of at least eight thousand and under thirty thousand, the council shall be elected for the following terms: The mayor shall be elected for a four-year term. The councilmen shall be elected for four-year terms except that at the first election the candidate receiving the highest number of votes shall serve a four-year term, the candidate receiving the second highest number of votes shall serve a three-year term, the candidate receiving the third highest number of votes shall serve a two-year term and the candidate receiving the fourth highest number of votes shall serve a one-year term. If any vacancy occurs in such office, the remaining members of the council shall appoint a person to fill such vacancy during the balance of the unexpired term. Such officers shall qualify and their terms shall begin on the first Monday after their appointment. The terms of office of the mayor and councilmen or aldermen in such city in office at the beginning of the terms of office of the mayor and councilmen first elected under the provisions of this section shall then cease and the terms of office of all other city officers, whether elective or appointive, in force in each such city, except as otherwise provided, shall cease as soon as the council shall by resolution declare.
§ 78.080, RSMo