Via Pew Research:
Christians are declining, both as a share of the U.S. population and in total number. In 2007, 78.4% of U.S. adults identified with Christian groups, such as Protestants, Catholics, Mormons and others; seven years later, that percentage has fallen to 70.6%. Accounting for overall population growth in that period, that means there are roughly 173 million Christian adults in the U.S. today, down from about 178 million in 2007.
The decline of Christians in the U.S. has corresponded with the continued rise in the share of Americans with no religious affiliation (religious “nones”). People who self-identify as atheists or agnostics (about 7% of all U.S. adults), as well as those who say their religion is “nothing in particular,” now account for a combined 22.8% of U.S. adults – up from 16.1% in 2007. The growth of the “nones” has been powered in part by religious switching. Nearly one-in-five U.S. adults (18%) were raised as Christians or members of some other religion, but now say they have no religious affiliation.
There are clear differences between certain demographic groups when it comes to religious affiliation. For example, younger adults are far more likely than older Americans to identify as religious “nones,” and men are more likely than women to be religiously unaffiliated. But despite these differences, the major trends seen in American religion since 2007 – the decline of Christians and rise of the “nones” – have occurred in some form across many demographic groups, including men and women, older and younger Americans, and people with different levels of education and different races and ethnicities.
The study also shows that Muslims now make up 0.9% of the population.
UPDATE: The Center For Inquiry celebrates.
“America is transforming before our eyes,” said Ronald A. Lindsay, President and CEO of the Center for Inquiry. “We are witnessing a tectonic shift from a nation nearly unified in its religiousness a generation ago, to an America where increasing numbers of Americans are rejecting religious doctrines and are living lives largely free of religious influence.”
“While it’s important to acknowledge that not all of the ‘Nones’ are nonbelievers, this sharp decline in religious affiliation points to a growing embrace of religious doubt among Americans,” said Lindsay. “Whether they consider themselves spiritual or atheist, the willingness to inquire and question religious assumptions is a promising sign for our nation’s future. We need critical thinkers, not followers.”
Added Lindsay, “Millennials make up the most secular generation America has ever known, which means that year by year, the grip of religion on American policy and culture will only continue to loosen. And a more secular America will be one that is closer the America envisioned in our founding documents: a nation governed by reason, whose policies are not influenced by religious beliefs.”