The United States, and yes, there is plenty.
I will never forget a test I gave in my class -- the day after Honor Society inductions -- when two inductees in the front row blatantly shared answers while I watched. I called them on it, only to have them do it again. I took their papers and wrote them up, asking that they be ejected from the Honor Society since they had none. No serious support from above. What message did that send?
Did I mention that I always had at least three versions of each test and that I always made that clear before every test?
Percentages... I would guess that among students, almost all cheat at some time of another, so 90%. I would also say that the truly ambitious slow down or stop doing it because it holds them back more and more as personal accountability in non-cheatable situations come increasingly into play.
I think there's cheating everywhere, not just in schools