Hello! I was raised an atheist but at the age of 18 converted to Christianity.
 It is the world's largest religion, over 2.4 billion in total.
What region are you talking about? Americas?
33% of the global population, not just Americas. But all over the world. 
Can you tell me whether the number is growing or declining?
They make up a majority in over 158 countries, but the actual growth cannot be verified
How about the last century? I bet it was more than 33%.
I don't know off the top of my head but secularization has been continuing for quite sometime even in the 19th century.