The United States, and yes, there is plenty. <br />
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? <br />
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