Marrying your first cousin is illegal in Montana under state law. The prohibition stems directly from the Montana Code Annotated, ensuring clear boundaries on familial relationships.​
Legal Prohibition
Montana Code Annotated (MCA) § 40-1-401 explicitly lists prohibited marriages, including those “between first cousins” alongside siblings, ancestors/descendants, and uncle/niece or aunt/nephew pairs. This applies regardless of half or whole blood relations. The statute voids such unions from inception, with no post-cohabitation validation except after impediment removal for other cases.
Permitted Relations
Second cousins and more distant relatives face no bans, as confirmed by marriage license forms requiring relationship disclosure only for scrutiny. First cousins once removed (e.g., your cousin’s child) are allowed, unlike tighter states. Half-first cousins remain prohibited under the broad wording.
Penalties and Enforcement
Attempting a cousin marriage yields no valid license—clerks reject applications upon relation disclosure. Post-ceremony, courts declare it void; bigamy charges could apply if undisclosed. No criminal penalties specified beyond civil invalidation, but fraud escalates risks. Common-law marriages follow the same rules.
Historical Context
Montana’s ban aligns with 31 other states restricting first-cousin unions, rooted in 19th-century eugenics concerns over genetic risks, though modern science shows low 3-4% added defect rates versus baseline. No reforms since codification; neighbors like Idaho and Wyoming mirror it.
Nationwide Comparison
Twenty states permit first-cousin marriage outright (e.g., California, New York); others add conditions like age 65+ or genetic counseling (e.g., Maine, Utah). Montana joins stricter bans in the Mountain West. Double first cousins face identical prohibitions everywhere applied.​
| State Category | Examples | First Cousins Allowed? |
|---|---|---|
| Fully Legal | CA, NY, FL | Yes ​ |
| Conditional | ME, UT, IN | With counseling/age ​ |
| Prohibited | MT, ID, TX | No |
Genetic and Social Factors
Offspring of first cousins carry 4-7% higher recessive disorder risk, per NIH data, versus 3-4% general population—prompting bans despite cultural acceptance elsewhere (e.g., 10% global rate). Montana prioritizes public health policy over individual choice. Social stigma persists in U.S. culture.​
Exceptions and Loopholes
No age, infertility, or counseling waivers exist in Montana, unlike flexible states. Out-of-state marriages may gain recognition if valid elsewhere, but residency complicates via domicile rules. Minors need consent but inherit prohibitions.​
Practical Steps
Marriage applicants disclose relations on forms; clerks enforce via MCA review. For valid unions, second cousins suffice. Legal advice recommended for edge cases like adoption. Interstate couples eye permissive venues like New Mexico.
Myths Debunked
- “Montana allows cousin cohabitation/relations”: True, no incest criminalization for adults, just marriage ban.
- “Once-removed okay always”: Yes in MT, but verify degrees.
- “Common-law overrides”: No, same prohibitions apply.​
Montana upholds a firm no on first-cousin marriage to balance tradition, health, and law.
SOURCES:
- https://archive.legmt.gov/bills/mca/title_0400/chapter_0010/part_0040/section_0010/0400-0010-0040-0010.html
- https://theamm.org/marriage-laws/montana/887
