In the UK first-cousin marriage is legal.
Also, the average Briton has 5 first-cousins, 28 second-cousins, 175 third-cousins, 1570 fourth-cousins, 17300 fifth-cousins and 174000 sixth-cousins.
That's on average 2 cousins per square mile.
So if you count all cousins as incestuous then you have your work cut out for you in avoiding them.