About 22% of Americans actually attend church in any given week. About 40% say that they do, however, when asked that question in surveys, and that data is often used to make the case that Americans are much more religious than people in other countries. The great exaggeration of church attendance is long standing, well documented and largely limited to Americans and Canadians. In reality, "Americans attended services about as often as Italians and Slovenians and slightly more than Brits and Germans."
The number of people who actually attend church in any given week is only a little larger than the number of people who claim no religious affiliation.