Prohibited marriages -- contracts
(1) The following marriages are prohibited:
(a) a marriage entered into prior to the dissolution of
an earlier marriage of one of the parties;
(b) a marriage between an ancestor and a descendant or
between a brother and a sister, whether the relationship
is by the half or the whole blood, or between first cousins;
(c) a marriage between an uncle and a niece or between
an aunt and a nephew, whether the relationship is by the
half or the whole blood;
(d) a marriage between persons of the same sex.
(2) Parties to a marriage prohibited under this section who
cohabit after removal of the impediment are lawfully married
as of the date of the removal of the impediment.
(3) Children born of a prohibited marriage are legitimate.
(4) A contractual relationship entered into for the purpose
of achieving a civil relationship that is prohibited under
subsection (1) is void as against public policy.
(Montana
Code Ann. Section 40-1-401)
Marriage
Only a marriage between one man and one woman shall be valid
or recognized as a marriage in this state.
(Montana Constitution, Article XIII, Section 7, approved by the electoriate on Nov. 2, 2004)