Is It Legal to Marry Your First Cousin? What US Law Actually Says

Is it legal to marry your first cousin? In the United States, the answer depends entirely on which state you are in. First-cousin marriage is fully permitted in a substantial minority of US states, prohibited outright in others, and allowed only under specific conditions in a further group. There is no single national rule, and there never has been.

That variation is the whole story, and it is why so much of what circulates online about this topic is unreliable. State legislatures amend marriage statutes, courts interpret them, and lists published a few years ago go stale. This guide explains how the rules are structured, what the conditions typically look like, what the genetic research actually shows, and exactly how to find the current answer for your own state.

This article is general information, not legal or medical advice. For a decision this consequential, confirm the current statute in your state and speak with a family law attorney licensed there.

Is It Legal to Marry Your First Cousin? The Three Categories of State Law

US states sort into three broad groups on first-cousin marriage: permitted, prohibited, and permitted with conditions attached.

Permitted. A significant number of states place no restriction on first cousins marrying. In these states, first cousins apply for a marriage license the same way anyone else does, and the county clerk does not treat the relationship as an impediment.

Prohibited. Other states include first cousins in the list of relationships within which marriage is void or voidable. In most of these, the marriage simply cannot be licensed. A smaller number have historically attached criminal penalties, though enforcement in modern practice is rare to nonexistent.

Permitted with conditions. This is the category most people do not know exists, and it is where the interesting variation lives. Some states allow first cousins to marry only if certain requirements are met. The conditions that appear in state law include:

• Age thresholds. Both parties must be over a stated age, typically well past the general marriage age. The reasoning is that the couple is unlikely to have biological children together.
• Proof of infertility. At least one party must show they cannot reproduce, sometimes requiring physician certification.
• Genetic counseling. The couple must complete counseling with a qualified genetic counselor or physician before a license is issued.
• Relationship-specific carve-outs. Some statutes distinguish first cousins from first cousins once removed, or treat adoptive and half-blood relationships differently from full-blood ones.

If you live in a conditions state, the practical question is not "is it legal" but "which specific requirement applies and how do I document it." That is a question for the county clerk's office and, ideally, an attorney.

Why the Law Varies So Much

The patchwork exists because marriage law in the United States has always been a state matter, and because most of the first-cousin restrictions were added during a specific historical window rather than inherited from older tradition.

English common law, which most American law descends from, did not prohibit first-cousin marriage. Neither did most of the American colonies. The bans came later, largely during the second half of the nineteenth century, when a wave of state legislatures added cousin marriage to their prohibited-degrees lists. The reasoning offered at the time drew heavily on the era's thinking about heredity and social improvement, and that intellectual context has not aged well.

This history explains something that surprises many Americans: the United States is unusual among Western countries in restricting cousin marriage at all. First-cousin marriage is legal throughout Canada, across most of Europe including the United Kingdom, and in much of Latin America, Asia, and Africa. It is restricted or prohibited in a number of other countries as well, including several in East Asia. The point is simply that the American restrictions are not a global norm, and they are not ancient.

What About Cousins Beyond the First Degree?

Restrictions in US law are aimed at first cousins and closer relationships. Second cousins, third cousins, and more distant cousins are not the target of these statutes.

First cousins once removed sit in an awkward middle position. This is your parent's first cousin, or your first cousin's child, a relationship our 1st cousin 1x removed guide covers in detail. A handful of state statutes name this relationship specifically; most do not, and where the statute is silent the relationship is generally not restricted. Because this is exactly the kind of detail that varies, it is a question worth putting to a clerk or an attorney rather than assuming.

Relationships that involve no blood connection at all are a different matter entirely:

• Step-cousins share no ancestor. Marriage laws based on consanguinity, meaning blood relationship, do not reach them.
• Cousins by marriage likewise share no ancestry.
• Adoptive relationships are the exception worth flagging. Some states extend prohibited-degree rules to adoptive relatives even where there is no biological connection, on the reasoning that the family relationship is what the law is protecting.

If you are not certain which category you are in, the free relationship calculator at cousinchart.com will tell you the exact term for your connection, which is the first thing any clerk or attorney will want to establish. Our cousin definition guide explains the numbering and the "removed" system if you need the groundwork first, and the 4th cousin piece covers how distant the relationship gets before it stops mattering to anyone.

Recognition of Marriages Performed Elsewhere

Many states will recognize a marriage that was validly performed in another state, even one they would not have licensed themselves. This is not universal, and it is not something to rely on without advice.

The general principle at work is called comity: states typically honor marriages that were lawful where they took place. In practice, a couple who married in a permissive state and later moved would usually find their marriage recognized. But there are real complications:

• Some states have evasion statutes aimed specifically at residents who leave the state to marry in a way their home state forbids, then return. The existence and reach of these provisions varies.
• Recognition for one purpose does not automatically mean recognition for all purposes. Tax treatment, inheritance, spousal privilege, and immigration can each be analyzed differently.
• A marriage that is void from the outset under a state's law is in a different legal position from one that is merely voidable.

Marrying in a permissive state to get around your home state's rule is a strategy that sounds simple and is not. If that is your situation, get advice from a family law attorney in your home state before, not after.

The Genetic Question, Honestly

The elevated risk to children of first cousins is real, and it is more modest than most people assume.

Here is the framing that actually helps. Every pregnancy carries some baseline risk of a significant birth defect or genetic condition, regardless of the parents' relationship. That background rate is commonly cited at roughly 3 to 4 percent. For children of first cousins, widely cited reviews of the research, including work published through the National Society of Genetic Counselors, place the risk at roughly 4 to 7 percent.

So the added absolute risk is on the order of a couple of percentage points. Reported estimates of that increase typically fall somewhere in the range of about 1.7 to 2.8 percentage points. In relative terms it is often described as roughly doubling the baseline, which sounds dramatic. In absolute terms it means the large majority of children born to first-cousin couples, well over 90 percent, are born without a significant genetic condition.

Some context worth holding alongside that number:

• The increase is comparable in scale to risks associated with other factors that are not treated as disqualifying, including maternal age past the mid-thirties.
• These are population averages. They describe a group, not a specific couple. A particular couple's actual risk depends on what is in their family history.
• The risk compounds meaningfully only when cousin marriage repeats across multiple generations in the same family line, which raises the overall level of shared ancestry well beyond that of a single first-cousin pairing.
• First cousins share about 12.5 percent of their DNA on average, and that figure varies from pair to pair. At the second cousin level the shared fraction drops to roughly 3 percent, and the genetic considerations become negligible.

The practical recommendation from genetics professionals is straightforward: see a genetic counselor. Not because the situation is alarming, but because a counselor can look at your actual family history, discuss carrier screening for conditions that run in your ancestry, and give you a number that means something for you specifically rather than for a population average. Carrier screening panels are widely available and far more informative than any general statistic.

None of the above is medical advice. It is a summary of published research, and your own circumstances need a professional who can see them.

How to Find the Answer for Your State

Do not rely on a list you found online, including tables in articles that look authoritative. Go to a primary or professional source.

Here is a reliable order of operations:

1. Read your state's own statute. Every state publishes its code online, usually free. Search your state's legislature or revisor of statutes website for the marriage chapter and look for the section on prohibited marriages or prohibited degrees of relationship. The statutory language is the actual law.
2. Call the county clerk or recorder in the county where you would apply for a license. They process these applications and can tell you what documentation, if any, they require.
3. Consult a family law attorney licensed in your state. This matters especially if your situation involves a move between states, a marriage performed elsewhere, an adoptive relationship, or anything touching inheritance or immigration.
4. Check the statute's effective date and any recent amendments. This area has seen legislative activity, and a provision that was accurate a few years ago may have been amended.

A quick note on the tables you will find elsewhere. Many are copied from one another, many are years out of date, and almost none flag which states attach conditions rather than a flat yes or no. A table that reduces this to two columns is hiding the part you most need to know.

Common Questions People Actually Have

Does a marriage license application ask about the relationship? Typically yes, in some form. Applications commonly include a declaration that the parties are not related within the prohibited degrees. Answering that honestly is important; a false statement on a license application creates its own problems.

What happens to an existing marriage if the couple moves? Generally nothing, but this is exactly where comity and evasion questions come in, and it is worth advice rather than assumption.

Is it a crime anywhere? Some state statutes have historically attached criminal penalties to marriage within prohibited degrees. Whether such provisions remain on the books, and whether they are ever enforced, varies. This is another reason to read the actual statute rather than a summary.

Does it affect immigration or spousal benefits? Federal agencies generally look to whether the marriage was valid where celebrated, but the analysis has wrinkles. Get advice specific to the benefit in question.

Frequently Asked Questions

Is it legal to marry your first cousin in the United States?

It depends on the state. First-cousin marriage is permitted in a substantial minority of US states, prohibited in others, and permitted subject to conditions such as an age threshold, proof of infertility, or completed genetic counseling in a further group. There is no federal rule. Check your state's current marriage statute or ask a family law attorney licensed there.

What conditions do some states attach to first-cousin marriage?

The most common are a minimum age for both parties, documentation that one party cannot have children, and a requirement that the couple complete genetic counseling before a license is issued. The exact requirements and how they must be documented vary from state to state, so the county clerk's office is the right place to confirm what you would need to produce.

Can first cousins who married in one state stay married after moving?

Usually, under the general principle that states recognize marriages that were valid where performed. It is not guaranteed, because some states have provisions aimed at residents who leave specifically to marry in a way their home state forbids, and recognition for one legal purpose does not automatically extend to every purpose. This is a situation that warrants an attorney rather than a general answer.

How risky is it genetically for first cousins to have children?

The baseline risk of a significant birth defect in any pregnancy is commonly cited at about 3 to 4 percent. For first-cousin couples, reviews of the research place it at roughly 4 to 7 percent, an absolute increase of somewhere around 1.7 to 2.8 percentage points. That is a real increase from a low base, and it means the large majority of children born to first-cousin couples do not have a significant genetic condition. A genetic counselor can give you a figure based on your actual family history rather than a population average.

Can second cousins marry?

Restrictions in US law are aimed at first cousins and closer relationships, so second cousins and more distant cousins are not the target of these statutes. Second cousins share roughly 3 percent of their DNA on average, which puts the genetic considerations close to those for an unrelated couple. As with everything here, your own state's statute is the authority.

Why is first-cousin marriage restricted in the US but not in most of Europe?

Because most American restrictions were added by state legislatures during the second half of the nineteenth century, drawing on the era's thinking about heredity. English common law, which American law largely descends from, did not prohibit it, and most European countries never adopted such bans. The United States is genuinely unusual among Western nations on this point.

Where do I find my state's actual law?

Every state publishes its statutes online for free through its legislature or revisor of statutes website. Look for the marriage chapter and the section on prohibited degrees of relationship. Read the current version and check for recent amendments, then confirm with the county clerk who would issue the license.