Three Out Of Ten Americans Are Non-Religious

The number of Americans who are not religious (people who have no desire to be a part of any organized religion) has remained steady for several years now at about three out of ten (29.4% in 2013). Some of these people are atheists, others are agnostics or skeptics, and some just don't care about religion one way or the other. This percentage is going to rise in the future, since each generation has a larger percentage of non-religious people than the generation that came before it -- and there is no indication that the trend will stop.
I think there has always been a fairly large portion of the population that was non-religious -- but in the past there was more social pressure to keep those beliefs quiet and go along with one's community peers. But with the internet, many people are now finding they are not alone in those non-religious beliefs, and that gives them the courage to express their own disbelief (especially among the young).
But just because about 30% say they are non-religious, that doesn't mean the other 70% are highly religious people. The percentage who identify a "very" religious is only 41.4% (or just a little more than four out of ten people). The rest (29.2%) say they are only "moderately" religious. And those are not just christian numbers, but include all religions. With numbers like these it simply doesn't make sense to write the christian religion into law -- as the fundamentalists want to do.
The chart below show the percentage of people claiming to be non-religious in each state (and the District of Columbia). Note that less people claim to be non-religious in the South -- probably because independent thinking is not as highly valued in the South as in other parts of the country.
Charts were made from information contained in yearly interviews done by the Gallup Poll. The 2013 information was taken between January 2nd and December 29th of 2013. A random national sample of 174,699 adults, and the survey had a margin of error of 1 point (with separate state surveys having a 3 point margin of error).
And here is the latest Public Religion Research Institute findings on religious beliefs by age group. Note that the non-religious increases with each generation.