30% sounds high, I am not sure how they determine what counts as a non-believer or non-religious person. I don't doubt that fewer people are religious than were in the 1990s, but I don't know if it's that high.
I live in the midwest now, and there are as many churches out here as there were in New York, which has a much higher population and population density. But I don't know how often people go to church. The area I'm in doesn't seem to be overtly religious. Maybe I just assume that most people are Christian because that was the USA I grew up in?