Roman Catholics Through the Years AD 30 to AD 2200 (est.)

From the March 3, 2013, Chicago Tribune "The power of the papacy."

30--  as many as 10,000
100--  170,000
300--  4.9 million
500--  12.7 million
800--  15.9 million
1000--  18.9 million
1350--  47.2 million
1500--  44.8 million
1650--  60.1 million
1750--  82.4 million
1800--  106.4 million
1850--  163.2 million
1900--  265.6 million
2000--  1.04 billion
2010--  1.17 billion

Interesting to note the big drop between 1350 and 1500 and the huge growth after 1850.