Mo. Rev. Stat. § 78.020: Organization.

That any city of the third class, including any such city acting under special charter or any city now having or which may hereafter have a population entitling them to become cities of the third class, may become organized as a city under the provisions of sections 78.010 to 78.420 by proceeding as herein provided, unless authority for the adoption of the plan of city government authorized by said sections be contained in the order incorporating such city, in which event an election shall not be necessary.