Mo. Rev. Stat. § 451.022: Public policy, same sex marriages prohibited — license may not be issued.

1. It is the public policy of this state to recognize marriage only between a man and a woman.

2. Any purported marriage not between a man and a woman is invalid.

3. No recorder shall issue a marriage license, except to a man and a woman.

4. A marriage between persons of the same sex will not be recognized for any purpose in this state even when valid where contracted.