Mo. Rev. Stat. § 115.609: County or city committee members, when elected (St. Louis City and County).

In each city not situated in a county and in each county which has over nine hundred thousand inhabitants, all members of the county or city committee shall be elected at the primary election immediately preceding each gubernatorial election and shall hold office until their successors are elected and qualified. In each other county, all members of the county committee shall be elected at each primary election and shall hold office until their successors are elected and qualified.