Mo. Rev. Stat. § 451.115

Every person who shall solemnize any marriage, having knowledge of any fact which renders such marriage unlawful or criminal in either of the parties under any law of this state, or, having knowledge or reasonable cause to believe that either of the parties shall be under the age of legal consent, or is prohibited by section 451.020 from entering into such marriage, or where to his knowledge, any other legal impediment exists to such marriage, and every person not authorized by law to solemnize marriages who shall falsely represent that he is so authorized, and who, by any pretended marriage ceremony which he may perform, shall deceive any innocent person or persons into the belief that they have been legally married, shall, on conviction, be adjudged guilty of a class C misdemeanor.