Mo. Rev. Stat. § 568.010: Bigamy — penalty.

1. A married person commits the offense of bigamy if he or she:

(1) Purports to marry another; or

(2) Cohabits with one whom he or she entered into a bigamous marriage in another jurisdiction.

2. A married person does not commit bigamy if, at the time of the subsequent marriage ceremony, he or she reasonably believes that he or she is legally eligible to remarry.

3. The defendant shall have the burden of injecting the issue of reasonable belief of eligibility to remarry.

4. An unmarried person commits the offense of bigamy if he or she:

(1) Purports to marry another knowing that the other person is married; or

(2) Cohabits with one whom he or she entered into a bigamous marriage in another jurisdiction.

5. The offense of bigamy is a class A misdemeanor.