Marrying a first cousin is illegal in some states while others allow the marriages under certain conditions. For example, North Carolina prohibits double-cousin marriages but allows first cousin marriages.
As of 2014, 25 states prohibit first cousin marriages. These states include Idaho, Iowa and Texas. Six states allow first cousin marriages but place restrictions on the marriages. One example is Illinois. In this state, the marriage is only legal if both people are 50 or older or one is unable to reproduce. First cousin marriage is legal in the remaining states, but it is frowned upon in most societies.