Utah Code § 76-7-101.5: Child bigamy -- Penalty.

(1) An actor 18 years of age or older is guilty of child bigamy when, knowing he or she has a wife or husband, or knowing that a person under 18 years of age has a wife or husband, the actor carries out the following with the person who is under 18 years of age:

(a) purports to marry the person who is under 18 years of age; and

(b) cohabitates with the person who is under 18 years of age.

(2) A violation of Subsection (1) is a second degree felony.