C.R.S. § 18-6-201: Bigamy.

(1) A married person who, while still married, marries or enters into a civil union in this state with another person commits bigamy, unless as an affirmative defense it appears that at the time of the subsequent marriage or subsequent civil union:

(a) The accused reasonably believed the prior spouse to be dead; or

(b) The prior spouse had been continually absent for a period of five years during which time the accused did not know the prior spouse to be alive; or

(c) The accused reasonably believed that he or she was legally eligible to remarry or legally eligible to enter into a civil union.

(1.5) A person who is a partner in a civil union, while still legally in a civil union, who marries or enters into another civil union in the state with another person other than a current partner in a civil union commits bigamy, unless as an affirmative defense it appears that at the time of the subsequent marriage or subsequent civil union:

(a) The accused reasonably believed the prior partner to be dead; or

(b) The prior partner had been continually absent for a period of five years during which time the accused did not know the prior partner to be alive; or

(c) The accused reasonably believed that he or she was legally eligible to marry or legally eligible to enter into a civil union.

(2) Bigamy is a class 2 misdemeanor.