Details, from a new Pew study:
The study finds that there are 2.18 billion Christians of all ages in more than 200 countries around the world, representing nearly a third of the estimated 6.9 billion 2010 global population. Christians are so geographically widespread that no single continent or region can indisputably claim to be the center of global Christianity.
In 1910, two-thirds of the world’s Christians lived in Europe (according to historical data from the Center for the Study of Global Christianity at Gordon-Conwell Theological Seminary in Massachusetts). Today, the Pew study finds, only about a quarter of all Christians (26 percent) live in Europe (26 percent). A plurality — more than a third (37 percent) — now reside in the Americas. About one in every four Christians (24 percent) lives in sub-Saharan Africa and about one-in-eight (13 percent) is found in Asia and the Pacific.
In the last 100 years, the number of Christians around the world has more than tripled from historical estimates of approximately 600 million in 1910 to more than 2 billion today. But the world’s overall population has also risen rapidly, from an estimated 1.8 billion in 1910 to 6.9 billion in 2010. As a result, Christians make up about the same portion of the world’s population in 2010 (32 percent) as they did a century ago (35 percent).
This apparent stability, however, masks a momentous shift. Although Europe and the Americas still are home to a majority of the world’s Christians (63 percent), that share is much lower than it was in 1910 (93 percent). The proportion of Europe’s population that is Christian dropped from 95 percent in 1910 to 76 percent in 2010, while the proportion of the overall population in the Americas (North America, Latin America and the Caribbean, combined) that is Christian fell from 96 percent to 86 percent. Over the same period, however, Christianity grew enormously in sub-Saharan Africa and significantly in the Asia-Pacific region, where there were relatively few Christians at the beginning of the 20th century. The share of the population that is Christian in sub-Saharan Africa climbed from 9 percent in 1910 to 63 percent in 2010, while in the Asia-Pacific region it rose from 3 percent to 7 percent.