Half of the world’s 1.28 billion Catholics are found in 10 countries
The global Catholic population grew by 7.4 percent from 2010 to 2015, rising to 1.285 billion, according to a Vatican estimate.
Interestingly enough, nearly 56 percent of the Catholic population lives in 10 countries, with the United States topping out in fourth place:
Those numbers alone, however, don’t seem to paint a complete picture of the state of Catholicism. For one, the survey appears to tally baptized Catholics who could one day decide to leave the Church.
In many countries, the vast majority of the Catholic population doesn’t attend Mass weekly, which creates a fine line between counting who’s still Catholic and who left the faith.
Pew Research Center has its own counts as well, but it’s not a global survey. At the end of the day, it’s probably unlikely we’d get an accurate bean count for a billion people.