It's the number one religion (by proportion of adherents) in the states of Washington and Idaho; it's the number two religion in California, Utah, Massachusetts and Arkansas. In most states, in fact, it ranks as the #2 or #3 belief, and in only a few is it #4 or #5. Nationwide, it ranks #3 overall, just behind Baptist (#2) and Catholic (#1). Yet very few elected officials profess this faith, and a significant plurality of US voters say that they'd never vote for someone who believes this. What is this religion?
It's no religion at all.
Much to the surprise of both the very religious and the entirely irreligious, non-theism consistently shows up as the second or third most popular belief across most states. According to the American Religious Identification Survey (PDF), assembled by the Graduate Center of the City University of New York in 2001, over 14% of US citizens profess themselves to be atheist, agnostic, humanist or secular; this compares to 16% Baptist, and 24.5% Catholic. This map from USA Today shows the breakdown by state (Flash required).
It's worth remembering this in light of recent statements by Sen. Barack Obama about the importance of religion to the Democratic party. Non-believers aren't just a tiny fringe element in American society, and they aren't just found in coastal "blue states." Non-religious people make up a higher percentage of the populations of Idaho, Montana, and Nevada than they do of those of California, Massachusetts or New York. This isn't the narrative we're given by popular culture or media, but it's reality.
I find this useful info for those of us thinking about the future for this reason: the stories we're told about how a society works may not match the reality, and we shouldn't build our models and scenarios based on what we assume to be true.