Mo. Rev. Stat. § 451.100: Marriages solemnized by whom.

Marriages may be solemnized by any clergyman, either active or retired, who is in good standing with any church or synagogue in this state. Marriages may also be solemnized, without compensation, by any judge, including a municipal judge. Marriages may also be solemnized by a religious society, religious institution, or religious organization of this state, according to the regulations and customs of the society, institution or organization, when either party to the marriage to be solemnized is a member of such society, institution or organization.