truthaboveknow ledge,
I personally don't know of any in america. the only extent I've known of is same clan dating, which aren't related in any means except for the same surname. h/e, I do know it was a customary in ancient times and in very small, isolated villages, which makes sense. also, beliefs and lifestyles sets in, and whereabouts in those places, to some, it may still be acceptable.
as the saying "My eyes recognize you as my sister-in-law, but my fists will not recognize you". - Wu Song