Mo. Rev. Stat. § 72.210
When two or more cities in this state, each containing a population of less than five hundred thousand inhabitants, adjoining and contiguous to each other in adjoining counties shall be desirous of being consolidated, it shall be lawful for them to consolidate under one government of the highest class under which either of said cities is organized and take the name of said city in the same manner and subject to the provisions of this chapter prescribed for the consolidation of adjoining cities in the same county and furnishing bonds by those petitioning for such elections, the subdivisions of the consolidated city into wards and the calling of an election for officers in such consolidated city shall be done by the respective county commissions of the counties in which such cities are situated and said elections shall be held simultaneously on the same day.
§ 72.210, RSMo