Each state has the right to create its own laws about certain matters. One of the areas where states have a lot of jurisdiction is in the realm of marriage and divorce. Some states may allow a marriage that would not be considered legal in another location. For example, some states allow men and women to marry their relations. While no one can legally wed a brother, sister, parent, aunt, uncle, niece, or nephew in America but some states allow people to marry their cousins. In Alabama, Alaska, California, Colorado, Connecticut, Florida, Georgia, Hawaii, Maryland, Massachusetts, New Jersey, New Mexico, New York, Rhode Island, South Carolina, Tennessee, Vermont, and Virginia, cousins can marry without running into any complications with the law. One source says that 1/1,000 Americans will marry a cousin.
According to the National Conference of State Legislation, 25 states prohibit marriage between first cousins, making this an entirely split issue. North Carolina is unique in that they allow first-cousin marriages but prohibit second-cousin ones. Six states will allow a first-cousin marriage in special circumstances. In Arizona and Wisconsin, the cousins must be over 65 in order to wed, or one of them must be unable to reproduce children. In Illinois, the same concept applies but the cousins must be at least 50. In Indiana both partners must be over 65. In Maine, the couple can get married but they need to obtain a physician's certificate and undergo genetic counseling. This is because there can be an increased risk for birth defects when cousins marry.
While kissing cousins is a traditional concept, instances have shown that men and women who are closely related can produce offspring with genetic disabilities. Recently, a cousin couple in Asia produced a child with six limbs, showing why a cousin marriage can become a serious concern. Admittedly, The National Society of Genetic Counselors says that the increased risk for a genetic defect among cousins is only an extra 1.7 to 2.8 percent. This is about the same as the genetic defect risk for any pregnant woman over 40. In almost every situation, cousins are the closest relations allowed to marry. No man may marry his sister, aunt, mother, or another female relative in his family. This is the same for women, and is enforced by the law. Any illegal marriage along these lines is normally rendered incestuous, and can come with serious consequences.
Every state except for North Carolina allows men and women to marry a second cousin. Another common occurrence is men or women who fall in love with their step-siblings. While this may sound a bit odd, the two children are not related. Step siblings are from one set of parents and integrated into another set. Because there is no blood relation between the two, there are no laws that bar step-siblings from getting married. Half-siblings, however, have the same bloodlines because they have one parent in common. In this case, the couple would not be allowed to wed. When it comes to adopted siblings, people often have questions. They are not related by blood at all, but are legally listed as siblings. According to the US marriage laws, men and women are not allowed to marry if they are legal siblings, even if they are not blood related.
Most governments believe that if a brother and sister have the same parents legally than they are considered siblings. In some states the issue is more subjective than others. For example, in Colorado the marriage statutes do not have any writing considering adopted siblings. Therefore adopted siblings who want to marry may want to check in with the law there. Internationally, countries like Sweden permit this sort of marriage in rare circumstances. If you have questions about a marital union, then you should talk to a lawyer who works on cases in your jurisdiction. He may be able to help you find out whether or not your marriage would be legally recognized.