Cousin marriage laws by state fall into three groups: 18 jurisdictions allow first-cousin marriage with no special rules, six allow it only if the couple meets age, fertility, or counseling conditions, and 27 states prohibit it outright. Because marriage is governed at the state level, where you apply for the license decides the answer. Moving afterward can create its own problems, since some banning states refuse to recognize these marriages even when they were legal where performed.
States Where First-Cousin Marriage Is Legal
The following 17 states and the District of Columbia place no special restrictions on first cousins beyond the standard marriage license requirements:
- Alabama
- Alaska
- California
- Colorado
- Florida
- Georgia
- Hawaii
- Maryland
- Massachusetts
- New Jersey
- New Mexico
- New York
- Rhode Island
- South Carolina
- Vermont
- Virginia
- District of Columbia
North Carolina also allows first-cousin marriage, with one exception: marriages between double first cousins are void. Double first cousins share both sets of grandparents, which happens when two siblings from one family marry two siblings from another. North Carolina lists double first cousins alongside closer relatives whose marriages are prohibited.1North Carolina General Assembly. North Carolina General Statutes Chapter 51, Article 1
Connecticut permitted first-cousin marriage until October 1, 2025, when a new law took effect making first cousins ineligible to marry. Marriages between first cousins performed in Connecticut before that date remain valid.2Connecticut General Assembly. AN ACT PROHIBITING FIRST COUSIN MARRIAGE
States That Allow First-Cousin Marriage With Conditions
Six states permit the marriage only when specific age, fertility, or counseling requirements are met. Most of these conditions reduce to one idea: the couple is unlikely to have biological children together.
Age and Fertility Rules
Arizona prohibits first-cousin marriage by default but allows it when both parties are 65 or older. Cousins under 65 can marry with the approval of a superior court judge, provided one of them can demonstrate an inability to reproduce.3Arizona Legislature. Arizona Revised Statutes Title 25 Section 25-101 – Void and Prohibited Marriages
Indiana takes a simpler approach. First cousins may marry only if both are at least 65, with no alternative path based on infertility.
Illinois allows first-cousin marriage when both parties are at least 50. Cousins of any age can marry if one provides a physician’s certificate confirming permanent and irreversible sterility.
Utah uses a two-tier system. First cousins can marry without restriction if both are 65 or older. If both are at least 55 but under 65, they need a district court finding that one of them is unable to reproduce.4Utah Legislature. Utah Code Title 81 Chapter 2 Part 4 Section 402 – Incestuous Marriages Void
Wisconsin allows the marriage when the woman has reached age 55. Regardless of age, first cousins may also marry if either party submits a physician’s affidavit confirming permanent sterility.5Wisconsin State Legislature. Wisconsin Statutes Section 765-03 – Who Shall Not Marry; Divorced Persons
Genetic Counseling in Maine
Maine takes a different approach. Rather than imposing age or fertility conditions, it requires first cousins to obtain a physician’s certificate of genetic counseling before they can receive a marriage license.6Maine State Legislature. Maine Revised Statutes Title 19-A Section 701 – Prohibited Marriages; Exceptions Cousins who complete it can marry regardless of age or fertility.
States That Prohibit First-Cousin Marriage
The remaining 27 states ban first-cousin marriage outright. A county clerk in any of these states will not issue a license to first cousins under any circumstances:
- Arkansas
- Connecticut (as of October 2025)
- Delaware
- Idaho
- Iowa
- Kansas
- Kentucky
- Louisiana
- Michigan
- Minnesota
- Mississippi
- Missouri
- Montana
- Nebraska
- Nevada
- New Hampshire
- North Dakota
- Ohio
- Oklahoma
- Oregon
- Pennsylvania
- South Dakota
- Tennessee
- Texas
- Washington
- West Virginia
- Wyoming
Minnesota’s prohibition includes a narrow carve-out for marriages permitted by the established customs of aboriginal cultures, but the ban applies to everyone else.7Minnesota Office of the Revisor of Statutes. Minnesota Statutes Section 517.03 – Prohibited Civil Marriages
Half-Cousins and Second Cousins
The rules above cover full first cousins. Half-first cousins share only one grandparent, and many states that prohibit full first-cousin marriage treat half-cousins differently; in a number of them, half-cousin marriage is legal. Second cousins, who share great-grandparents rather than grandparents, can marry everywhere in the United States. No state prohibits second-cousin marriage.
If you’re unsure which category applies, the question is how many grandparents you share. Two shared grandparents makes you full first cousins. One makes you half-first cousins. Zero shared grandparents but one or two shared great-grandparents makes you second cousins.
Criminal Penalties and Void Marriages
A first-cousin marriage in a prohibiting state isn’t just unrecognized. In some states it can trigger criminal charges, and the severity varies widely.
Kentucky classifies a sexual relationship between first cousins as a felony under its incest statute, even between consenting adults.8Kentucky Legislative Research Commission. Kentucky Revised Statutes 530.020 – Incest Other states treat the offense as a misdemeanor, and some prohibit the marriage without attaching any criminal penalty to the relationship itself. The difference usually depends on whether the state’s incest statute specifically names first cousins or stops at closer relatives.
Prohibited marriages also vary in how they’re classified. Some states declare first-cousin marriages “void,” meaning the marriage is treated as though it never existed and requires no court action to dissolve. Others classify them as “voidable,” meaning the marriage is considered valid until a court annuls it. The practical difference matters. A void marriage can affect property ownership and inheritance rights retroactively, while a voidable marriage generally remains valid until someone successfully challenges it in court.
Marrying in One State and Moving to Another
The U.S. Constitution’s Full Faith and Credit Clause generally requires each state to recognize the official acts of every other state.9Legal Information Institute. U.S. Constitution Annotated Article IV Section 1 – Overview of the Full Faith and Credit Clause Marriage recognition is less straightforward in practice. States can invoke a “public policy exception,” refusing to recognize an out-of-state marriage that conflicts with their own legal principles.
How this plays out varies. Some prohibiting states will still recognize a first-cousin marriage legally performed elsewhere, particularly if the couple didn’t travel specifically to evade their home state’s ban. Others explicitly void such marriages regardless of where they were performed. Delaware, for example, declares that a marriage between first cousins obtained or recognized outside the state does not constitute a legal or valid marriage within Delaware.
Federal immigration authorities apply a similar analysis. USCIS looks at whether the marriage was valid where performed and whether the couple’s state of residence would recognize it. A first-cousin marriage performed in Colorado was accepted for a couple residing in Illinois because Illinois had no strong public policy against recognizing such unions. A first-cousin marriage between Wisconsin residents who traveled to South Carolina specifically to evade Wisconsin’s ban was rejected.10U.S. Citizenship and Immigration Services. USCIS Policy Manual Volume 6 Part B Chapter 6 – Spouses
Federal Benefits, Taxes, and Social Security
Federal agencies generally look to the law of the state where a couple lives to decide whether a marriage is valid for benefits purposes. That creates real consequences when a first-cousin couple moves from a permitting state to a prohibiting one.
The Social Security Administration determines survivor benefits based on whether the courts of the deceased worker’s state of residence would have recognized the marriage. If the worker was living in a state that bans first-cousin marriage at the time of death, the surviving spouse may be denied benefits. SSA has specifically ruled that the relationship between first cousins is a “substantive” barrier to marriage rather than a procedural defect, so the agency’s fallback provisions for good-faith marriages don’t apply.11Social Security Administration. SSR 63-20 – Relationship – Validity of Marriage Between First Cousins
For tax purposes, a marriage that a court has annulled is treated as though it never happened. The IRS requires amended returns for all tax years affected by the annulment, changing the filing status to single or head of household.12Internal Revenue Service. Publication 504 – Divorced or Separated Individuals If you filed jointly during years the marriage was later declared void, refiling can have a significant financial impact.
Why Some States Restrict Rather Than Ban
The conditions imposed by states like Arizona, Utah, and Wisconsin reflect a specific concern: the elevated genetic risk to biological children of first cousins. Research in genetics has found that unrelated parents face roughly a 2 to 3 percent chance of having a child with a significant genetic condition. For first cousins, that figure rises to about 5 to 6 percent. The increase is real but modest, which helps explain why some states opted for conditional permission rather than an outright ban.
States that set age thresholds at 50, 55, or 65 are using age as a proxy for reproductive capacity. States that accept medical proof of sterility address the concern directly. Maine’s genetic counseling requirement represents a third philosophy: give the couple full information and let them decide.