Originally Posted by Gibonius
I suppose only the act of marriage is illegal, not being married. Otherwise you could legally get married in one state, then be a felon by moving across state lines.
Being married to your cousin is not a criminal offense anywhere in the US. Having sex with your cousin is illegal in a handful of states, and cousin marriages are void in many others. There are a few states where it's not a valid marriage if you marry there, but if you get married somewhere else and then move there it's valid. West Virginia, for example.
Also, we are all at least 50th cousins with each other.