Mo. Rev. Stat. § 81.050
At the next municipal election in all cities and towns under special charters having one thousand inhabitants and less than three thousand inhabitants, and every two years thereafter, there shall be elected the officers as specified in said charters to be elected, each of whom shall hold his office until his successor is elected and qualified; except that any such city may provide by ordinance that two councilmen shall be elected each year for a term of two years. At the first election held after the passage of any such ordinance the two councilmen receiving the highest number of votes shall hold office for two years each and the two receiving the next highest number of votes shall hold office for one year each; and thereafter two councilmen shall be elected each year for terms of two years each.
§ 81.050, RSMo