Mo. Rev. Stat. § 81.150
In all cities and towns under special charter which have not less than ten thousand inhabitants and not more than thirty thousand inhabitants, there shall be elected two aldermen from each ward, who shall hold office for a term of four years; provided, that at the next general election for municipal officers to be held in any such city or town there shall be elected one alderman from each ward, who shall serve for a term of four years, and in the year next following such election, at the time of holding the general election for municipal officers in such city or town, there shall be elected one alderman from each ward, who shall serve for a term of one year, after which election there shall be elected, at each succeeding general election for municipal officers in such city or town, one alderman from each ward, who shall serve for a term of four years.
§ 81.150, RSMo
RSMo 1939 § 7471