The Pew Research Center published a study analyzing the prevalence of self-described former Catholics in 24 countries.
Former Catholics are rare in Poland: 96% of Poles say they were raised Catholic, 92% say they are still Catholic, and 4% describe themselves as former Catholics. In the United States, on the other hand, there are almost as many self-identified former Catholics as self-identified Catholics: 30% of Americans say they were raised Catholic, 17% say they are still Catholic, and 13% describe themselves as former Catholics.