Marrying your third cousin is legal in all 50 states. No state’s marriage laws reach relatives as distant as third cousins, so you can apply for a license, marry, and live anywhere in the country without a special exception or workaround. The marriage is treated the same as one between two unrelated people.
What Counts as a Third Cousin
A third cousin is someone who shares the same set of great-great-grandparents as you, descending through a different branch of the family. First cousins share grandparents; second cousins share great-grandparents; third cousins go one generation further back. Your parent’s second cousin’s child is your third cousin.
The word “removed” describes a generational gap, not a different type of cousin. A third cousin once removed is either your third cousin’s child or one of your parent’s third cousins. These relationships are more distant still and carry the same legal status as a standard third cousin marriage.
Where States Draw the Line
Every state prohibits marriage between close blood relatives, but the prohibitions target a narrow set of relationships. Universal bans cover parent-child, sibling, and grandparent-grandchild unions. Most states also prohibit aunt-nephew and uncle-niece marriages. The only cousin-level restriction that appears in any state involves first cousins, and even that ban is not universal.
Roughly half of U.S. states prohibit first cousin marriage. A handful permit it only under specific conditions, such as both parties being over a certain age or unable to have children. The remaining states place no restriction on first cousins at all. A small number of states extend prohibitions to second cousins, and that is the outer limit anywhere in the country. No state restricts marriage between third cousins.
The pattern tracks genetic overlap:
- Siblings and parent-child: prohibited in all 50 states, roughly 50% shared DNA.
- Aunts/uncles and nieces/nephews: prohibited in the vast majority of states, about 25% shared DNA.
- First cousins: prohibited in roughly half of states, conditional in about six, fully legal in the rest; about 12.5% shared DNA.
- Second cousins: prohibited in a handful of states; about 3.1% shared DNA.
- Third cousins and beyond: legal everywhere; about 0.8% shared DNA.
By the time you reach third cousins, the connection is diluted enough that it falls entirely outside the scope of marriage regulation.
Applying for the Marriage License
Most marriage license applications do not ask specifically about blood relations. You’ll provide identification, Social Security numbers, information about any prior marriages, and signatures attesting that you’re legally eligible to marry. Some states ask applicants to affirm they are not closely related, but “closely related” in that context refers to the relationships that state actually prohibits. Third cousins are never on that list.
If a form does ask whether you’re related to your partner, answering honestly about a third cousin connection creates no problem. The relationship falls outside every state’s prohibited degrees. You won’t be denied a license, and no additional documentation or approval is required.
Moving Between States and Immigration
Because third cousin marriage is legal in every state, interstate recognition is never an issue. You can marry in one state and move to another without any legal complication. This contrasts with first cousin marriages, where the patchwork of state laws can create real questions about whether a marriage travels with the couple.
The same simplicity applies to immigration. When one spouse seeks a U.S. visa or green card through the marriage, USCIS looks at whether the marriage is consistent with the laws of the state where the couple lives or plans to live. Because a third cousin marriage is valid under every state’s law, USCIS treats it like any other spousal relationship.
Genetic Risk
Third cousins share an average of about 0.8% of their DNA, with a range of roughly 0.06% to 2.2% depending on the specific family tree.
For context, the baseline risk that any child is born with a significant congenital condition is about 2-3% in the general population. For first cousin couples, that risk rises by roughly 1.7-2.8 percentage points above baseline, bringing the total to about 4-6%. For third cousins, the added risk is so small that it is essentially indistinguishable from the general population baseline. Genetic counselors do not recommend special testing or screening for third cousin couples. The shared DNA is too minimal to meaningfully increase the odds that both parents carry the same recessive gene variant.
Double Third Cousins
Some couples turn out to be third cousins through two separate family lines rather than one. This can happen when, for example, two siblings from one family each married into the same other family a few generations back. Double third cousins share roughly twice the DNA of regular third cousins, around 1.6%. That is still far below the level at which genetic counseling becomes relevant, and the legal status is identical. A double third cousin marriage is permitted in every state without conditions.