RCW 9A.64.010: Bigamy.

(1) A person is guilty of bigamy if he or she intentionally marries or purports to marry another person when either person has a living spouse.

(2) In any prosecution under this section, it is a defense that at the time of the subsequent marriage or purported marriage:

(a) The actor reasonably believed that the prior spouse was dead; or

(b) A court had entered a judgment purporting to terminate or annul any prior disqualifying marriage and the actor did not know that such judgment was invalid; or

(c) The actor reasonably believed that he or she was legally eligible to marry.

(3) The limitation imposed by RCW 9A.04.080 on commencing a prosecution for bigamy does not begin to run until the death of the prior or subsequent spouse of the actor or until a court enters a judgment terminating or annulling the prior or subsequent marriage.

(4) Bigamy is a class C felony.