Yes, you can marry your third cousin anywhere in the United States. No state’s marriage laws restrict unions between third cousins, and there is no federal law on cousin marriage at any level. The prohibitions that do exist stop well short of a relationship this distant, so a third cousin marriage is treated the same as any other marriage between two unrelated adults.
Who Counts as a Third Cousin
Third cousins share a set of great-great-grandparents. The common ancestor is four generations back. Your parent’s second cousin is your third cousin, and your grandparent’s first cousin’s grandchild is also your third cousin. Many people have third cousins they’ve never met.
Genetically, third cousins share an average of about 0.78% of their DNA, with a range roughly between 0.06% and 2.2%.123andMe Customer Care. Average Percent DNA Shared Between Relatives At under 1% shared DNA, third cousins are, in practical terms, indistinguishable from unrelated people.
Where State Consanguinity Laws Actually Stop
Every state has laws that prohibit marriage between close relatives, but none of them reach third cousins. About 25 states prohibit first cousin marriage outright. A handful of others allow it only with conditions such as an age minimum or an inability to reproduce, and a few will recognize first cousin marriages performed elsewhere without allowing the ceremony locally.
Only about five states extend their prohibitions to second cousins. That is the outer edge of consanguinity restriction in the United States. If you are third cousins or more distantly related, you are outside every one of these laws. Even the clinical definition of a consanguineous marriage typically starts at second cousins or closer, so a third cousin marriage doesn’t cross that line either.2National Center for Biotechnology Information (NCBI). Consanguineous Marriage: Law and Public Health
Applying for the Marriage License
The license process is the same one every couple goes through. You apply at your local county clerk’s office, show identification, provide the required personal information, pay the filing fee, and sign a sworn affidavit. Fees generally run between about $20 and $110 depending on the state and county.
Some applications ask whether the applicants are related, or require a sworn statement that the couple is not related within a degree prohibited by law. You can answer honestly: you are related, but not within any prohibited degree. The affidavit is a legal document and false statements on it can constitute perjury, so give an accurate answer. If the form asks specifically about the relationship, a brief note that you share great-great-grandparents is usually all a clerk needs. No state requires genetic counseling, age conditions, or any other special step for third cousins.
If You Want a Religious Ceremony
Civil legality and religious permission are separate questions. If you’re planning a religious wedding, the officiating body may apply its own consanguinity rules.
The Roman Catholic Church treats consanguinity as a diriment impediment up to and including the fourth degree of the collateral line under its canonical system, which covers first cousins.3Vatican. Code of Canon Law – Book IV – Function of the Church Liber (Cann. 998-1165) Third cousins fall in the eighth degree, well outside the impediment, and no dispensation is required.
The Eastern Orthodox Church prohibits marriage between collateral blood relatives up to the seventh degree, which reaches second cousins. Third cousin marriages sit at the eighth degree and are permitted.4Eastern Orthodox Church in North America. A List of Prohibited Marriages in the Orthodox Church Most Protestant denominations don’t impose consanguinity rules beyond civil law, though individual congregations sometimes set their own policies.
Immigration and Federal Recognition
If one spouse is not a U.S. citizen, USCIS will recognize a marriage that was legally valid where it was performed and consistent with U.S. public policy.5USCIS. Chapter 6 – Spouses The agency does give closer scrutiny to marriages between close relatives, but that scrutiny targets first cousin marriages in states that prohibit them. The core question is whether the couple’s state of residence would refuse to recognize the union or treat the relationship as unlawful. Because no state prohibits third cousin marriage, that analysis comes out in the couple’s favor every time.