If we take Religion as any indication of irrationality then America should be one of the least rational countries in the world.

There are parts in Europe where there are many more non-believers, but those are not necessarily more rational. To a large extent it is environment, parents, friends etc. that determine religiosity or lack thereof. It seems that when people are gradually getting more rational, religion is not the first thing that gets thrown out the window. I notice that superstition, medical quakery and various supernatural beliefs are alive and well in secular Europe.

It'd be great if there were some survey comparing the degree to which such ideas flourish in different parts of the world.