No, it is not illegal to date your cousin anywhere in the United States. No state regulates who consenting adults spend time with romantically. The legal risk shows up elsewhere: in roughly nine states, sexual relations between first cousins are a crime, and about half of all states refuse to issue a marriage license to first cousins. So dating is fine everywhere; what you do after dinner, and whether you can ever marry, depends entirely on where you live.
Where the Line Actually Sits
Going out with a cousin, being seen together, calling each other partners, moving in as roommates in most states: none of that triggers a statute. The law doesn’t police the relationship itself.
Sex is the first place the line can appear. About nine states classify sexual intercourse between first cousins as incest. Penalties range from a misdemeanor to a felony carrying years in prison, thousands of dollars in fines, and in the most severe cases, sex offender registration. At least one state also criminalizes cohabitation between first cousins, meaning simply living together as a couple can be charged.
This is the part that catches people off guard. The common shorthand “it’s legal to date your cousin” is true as far as it goes, but it doesn’t carry over to a sexual relationship in every state. If you’re in a jurisdiction with an incest statute that reaches first cousins, the prohibition applies whether or not you ever apply for a marriage license.
State Laws on First-Cousin Marriage
States have landed in three very different places.
Roughly 19 states and the District of Columbia allow first-cousin marriage with no restrictions. First cousins apply for a license the same way any other couple would, and the clerk doesn’t ask about the family tree.
About half a dozen states permit the marriage with conditions attached, and every condition targets reproduction. The most common is an age floor, typically somewhere between 50 and 65, on the assumption that the couple is past childbearing years. Others require proof that one or both parties cannot have children. At least one state requires the couple to complete genetic counseling before a license will issue. Miss the condition and the clerk denies the license.
The remaining states prohibit first-cousin marriage outright. A clerk in those jurisdictions will not issue a license, and any resulting marriage is void from inception or voidable by court order. A smaller subset of these states goes further, treating the marriage itself as a criminal offense with penalties similar to the sexual-conduct crimes above. The map isn’t static: as recently as 2025, a state that had long permitted first-cousin marriage enacted a ban, grandfathering existing marriages. Check current law in your own state before relying on anything general.
Which Cousins the Law Targets
First cousins share a set of grandparents. Your aunt’s or uncle’s children are your first cousins, and this is the relationship the statutes focus on because of the closer genetic overlap.
A smaller number of states extend their prohibitions to first cousins once removed, meaning the child of your first cousin, or equivalently, your parent’s first cousin. Far fewer states reach this far.
Second cousins share great-grandparents rather than grandparents. Marriage and sexual relationships between second cousins are legal in all 50 states and the District of Columbia, and the same holds for anything more distant. If the common ancestor is more than two generations back, no state cares.
What Happens If You Marry In One State and Move to Another
Two first cousins marry legally in a permissive state, then move to one that bans the practice. Is the marriage still valid?
The default rule in American law, called the place-of-celebration doctrine, is that a marriage valid where it was performed is valid everywhere. Crossing a state line doesn’t dissolve your marriage.
The rule isn’t absolute. States can refuse to recognize an out-of-state marriage that violates their own public policy, and some states that ban first-cousin marriage have statutes explicitly declaring such unions void. That gives a court a basis to refuse recognition even when the marriage was perfectly legal where it took place.
Courts have been inconsistent in how they apply this. Some have upheld out-of-state cousin marriages even in states with their own bans. Others have refused recognition when the evidence showed the couple left the state only to get a license and came straight back. The distinction judges tend to draw is between couples who genuinely lived in the permissive state and couples who made a weekend trip to work around their home state’s law. If you’re in this situation, don’t assume recognition is automatic.
Federal Benefits and Taxes
Federal agencies don’t agree on how to decide whether your marriage counts, and that disagreement can be expensive.
The IRS uses the state where the marriage was celebrated. If you married your first cousin in a state that allows it, you can file a joint federal return even if you now live in a state that treats the marriage as void.1Internal Revenue Service. Publication 501 (2025), Dependents, Standard Deduction, and Filing Information
Social Security goes the other way, and this is where couples get hurt most often. The agency looks at the law of the state where the worker was domiciled when they applied for benefits or when they died. A couple married legally in a permissive state can still lose survivor benefits if the worker lived in a prohibiting state at death.2Social Security Administration. Social Security Act Section 216 The agency has specifically said that a cousin relationship is a substantive legal defect, and its good-faith marriage exception, which sometimes rescues people who unknowingly entered invalid marriages, does not cover couples who knew they were cousins.3Social Security Administration. SSR 63-20 – Section 216(h) Relationship – Validity of Marriage Between First Cousins
Employer-sponsored health insurance and retirement benefits under ERISA follow the IRS approach. If the marriage was valid where performed, the Department of Labor treats the spouse as a spouse for coverage purposes.4U.S. Department of Labor. Technical Release No. 2013-04 So your employer plan should cover your cousin-spouse even in a state that bans the practice. Social Security plays by different rules, and the gap can cost a surviving spouse tens of thousands of dollars over a lifetime.
Immigration Sponsorship
If a U.S. citizen or permanent resident wants to sponsor a cousin-spouse, USCIS generally recognizes first-cousin marriages that were legal where performed, but it also looks at whether the marriage is consistent with the public policy of the state where the couple lives or intends to live.5USCIS. USCIS Policy Manual Volume 6, Part B, Chapter 6 – Spouses The State Department applies a similar framework at consular interviews and can flag the marriage for additional review.6U.S. Department of State. 9 FAM 102.8 Family-Based Relationships
The factor that drives contested cases is the same one courts use for recognition disputes: did the couple travel to a permissive state specifically to get around their home state’s prohibition? A couple who genuinely lived in the permissive state and later moved has a much stronger case than one that crossed state lines for a license and immediately returned to a state that treats the marriage as void and criminal.