US state bans first cousin marriages but it remains legal in 16 other states

A US state is set to ban marriages between first cousins from next month, but it remains legal in 16 other states.

As of October 1, Connecticut will prohibit marriages between first cousins - individuals who share a common set of grandparents, meaning their parents are siblings - due to genetic and social concerns.

The new law, which was passed by both the Democratic and Republican Parties, does not impose penalties for existing marriages between first cousins that were valid before the law takes effect, and it likewise doesn’t retroactively void marriages already in place.

It only covers marriages starting from October 1, 2025, and only on 'knowingly' marrying a first cousin, so awareness of the relationship is part of the legal caveat.

Devin Carney, Connecticut State Representative (Republican), who proposed the bill, told the Connecticut Post: "Somebody actually sent me an article about it. Tennessee recently banned it. They passed a law to ban it.

A US state will be banning first cousin marriages from the start of next month (1 October) (Christoph Wagner / Getty Images)

"I was told it’s not banned in Connecticut, so I started looking into it and over 30 states do ban it, and Connecticut is not one of them."

Democrat State Representative Steve Stafstrom added: "We looked at it and saw we were sort of an outlier state that didn’t ban it.

"Science shows that procreation between first cousins increases the chances of birth defects. We also didn’t want to penalise or jeopardise any marriages that occurred when it was legal."

Connecticut will become the 26th US state to fully ban first-cousin marriages.

After catching light of the news, people rushed to social media to share their reactions - namely their shock that first-cousin marriages were still legal in many US states.

Connecticut will become the 26th US state to fully ban first-cousin marriages (SimpleImages / Getty Images)

One Instagram user questioned: "How is this still possible in 2025 America?"

"Why is it even legal in the first place?" wondered a second, while a third hit out: "Really? It’s still legal in 2025?! Gross."

A fourth echoed: "This is a thing????"

"It really took this long?" penned another.

And a final Instagram user added: "Why is a law needed? Isn’t that common sense?"

Research from the National Library of Medicine has shown that procreation between family members can cause a number of birth defects. These include limb deformities, heart conditions, premature birth, and neonatal mortality.

There are 16 other US states which still allow first cousins to get married (Getty Stock Images)

States where first-cousin marriage is allowed (no special additional restrictions)

These states allow first cousins to marry under normal marriage laws, as per LegalClarity.

• Alabama
• California
• Colorado
• Florida
• Georgia
• Maryland
• Massachusetts
• New Jersey
• New Mexico
• New York
• Rhode Island
• South Carolina
• Vermont
• Virginia
• North Carolina (with a restriction: “double first cousins” are not allowed)

States where first-cousin marriage is allowed (under special additional restrictions)

With that said, there are also several us states that allow first-cousin marriage only under specific restrictions or conditions, rather than allowing it freely. Laws differ by age, fertility, counselling, etc.

In Arizona, first cousins may marry only if both are 65 or older, or if one is infertile, while in Illinois, it's allowed only if both parties are 50 or older, or if one of them is permanently and irreversibly sterile.

Likewise, for Indiana, it's only allowed if both are at least 65 years old, while in Maine, first cousins need to obtain a physician’s certificate for genetic counselling beforehand.

In Utah, yet again, it's allowed if both parties are 65 or older, or if both are at least 55 and one is unable to reproduce, and lastly, in Wisconsin, it's only allowed if the woman in the marriage is at least 55 or if one of the parties is permanently sterile.

The bill was passed due to genetic and social concerns (Manu Vega / Getty Images)

States prohibiting first-cousin marriage

"A significant number of states have laws that explicitly prohibit the marriage of first cousins. In these jurisdictions, a marriage license will not be issued to first cousins under any circumstances," LegalClarity explains.

The states that have an outright ban on first-cousin marriage include:

• Arkansas
• Delaware
• Idaho
• Iowa
• Kansas
• Kentucky
• Louisiana
• Michigan
• Mississippi
• Missouri
• Montana
• Nebraska
• Nevada
• New Hampshire
• North Dakota
• Ohio
• Oklahoma
• Oregon
• Pennsylvania
• South Dakota
• Tennessee
• Texas
• Washington
• Wyoming

These prohibitions are typically found within state statutes that define prohibited degrees of kinship for marriage. Furthermore, some of these states may classify such a marriage as a criminal offence.