Via Pew Research:
Earlier this summer, on World Population Day, we explained that half of the world’s population lives in just six countries. In many cases, the world’s major religious groups are even more concentrated, with half or more of their followers living in one or a handful of countries. For several years, demographers at the Pew Research Center have been studying the demographic characteristics of eight groups: Buddhists, Christians, adherents of folk religions, Hindus, Jews, Muslims, the religiously unaffiliated and followers of other religions. While Christians and Muslims are more widely distributed around the world, the other groups have a majority of their populations in just one or two nations, according to 2010 estimates from our Global Religious Landscape report.
While there continues to be much attention paid to the growth of the religiously unaffiliated population in Europe and North America, more than half (62%) of the world’s 1.1 billion unaffiliated people live in one Asian country: China. China also is home to 50% of the world’s 488 million Buddhists and 73% of the 405 million global adherents of folk religions. Since China is the world’s most populous nation, it may not be altogether unexpected that it has a lot of people in a variety of categories. While China accounts for 19% of the world’s overall population, it is home to majorities of all Buddhists, unaffiliated people and adherents of folk religions.
More maps are at the link.