Sure thing. I have been a Catholic my entire life and have filled out the little piece of paper every year since I reached adulthood and was off on my own, even during the 20+ years I was in military service.
If that’s not good enough for you, I am sure you are perfectly capable of doing your own research without me having to hold your hand. Google is always a good place to start:
http://www.google.com/search?q=catholic+church+census&hl=en&client=safari&rls=en-us&start=10&sa=N
Other than that, I don’t really care whether you believe it or not because, as they say, it is what it is, and doesn’t really mean anything one way or another (denomination membership or trends that is) anyways.
(NOTE: the fastest growing religion in the world is Islam (might be the largest too...don’t remember)..does that mean it’s the best or true religion? I hardly think so.)