Is There a Law Against Marrying Your Cousin?

In the United States, the legality of cousin marriages varies from state to state; there is no single federal law that rules on the legality of cousin marriages. Approximately half of the United States allow first cousin marriages (also known as consanguineous marriages), and approximately half ban them. In some states, cousin marriages are perfectly legal; in others, it may constitute a criminal offense. Even in states where cousin marriages are legal, there may be additional restrictions that disallow some cousin couples from marrying.

Cousin marriages is a criminal offense, punishable by law, in Texas, the Dakotas, Oklahoma, and Nevada. It is illegal, but not a criminal offense, in states such as those in the Pacific Northwest and throughout much of the Midwestern United States. It’s entirely legal in states such as Alaska, California, the Florida panhandle states, South Carolina, and the New England states, in addition to a few others. The legality of such unions may come with exceptions; in Arizona, for example, first-cousin marriage is legal only if both parties are over 65, or if one is infertile. In Maine, cousin marriages are legal only if the couple can provide proof that they’ve undergone genetic counseling from a licensed genetic counselor.

The legality of cousin marriages becomes more lax outside the case of first cousins marrying (that is, cousins who share a set of grandparents). In Oklahoma, for instance, first-cousin marriages are illegal, but half-cousin marriages are permissible.

In addition to banning consanguineous marriages in their own state, some states may not recognize such marriages performed in other states. In New Hampshire, where cousin marriages are disallowed, all consanguineous marriages performed out of state are considered void as well. This means that a couple in a consanguineous marriage who move to New Hampshire from a state like Alaska will find their marriage voided in their new home state.

How long have laws prohibiting first-cousin marriages existed?

Cousin marriages have been a common practice historically throughout much of the Western world, especially among royal families, who often intermarried among cousins to maintain their bloodline. The tradition of cousin marriages followed early settlers to America. Prior to the Civil War, cousin marriages were legal across the United States. A number of medical studies conducted throughout the 1800s suggested that the offspring of cousin marriages were more likely to develop certain medical maladies such as blindness, although many of these studies were heavily disputed. Nonetheless, by the 1880s, 13 states and territories had outlawed cousin marriages.

Although medical science has advanced far beyond what it knew in the 1800s, the belief that children of consanguineous marriages will suffer health defects still influences US cousin marriage law. States that permit cousin marriages may only do with the condition that at least one of the parties be sterile prior to the marriage. This is true in Illinois, Indiana, and Utah, among others.

Where else are there laws against marrying your cousin?

Interestingly, the United States is one of the few nations in the world to have laws against consanguineous marriages. Cousin marriages are entirely legal throughout Canada, Europe, South America, Australia, the Middle East, Russia, and much of Northern Africa.