Mo. Rev. Stat. § 72.090
Provided, that any city or town of the state of Missouri, not incorporated, having sufficient population to entitle it to become a city of the third class, in making application for incorporation as a city of the third class, may include in its petition for such incorporation a request that it be authorized to avail itself of the provisions of sections 78.010 to 78.420, and the county commission, in passing upon such application, shall have power in its order of incorporation to authorize said city to be governed by the provisions of sections 78.010 to 78.420 as fully as if the provisions of sections 78.010 to 78.420 had been adopted by a formal election of the inhabitants of the territory comprised therein; and thereupon such county commission shall appoint the officers of such city provided by sections 78.010 to 78.420.
§ 72.090, RSMo
RSMo 1939 § 6217