Over all, the religiously unaffiliated number 56 million and represent 23 percent of adults, up from 36 million and 16 percent in 2007, Pew estimates. Nearly half of the growth was from atheists and agnostics, whose tallies nearly doubled to 7 percent of adults. The remainder of the unaffiliated, those who describe themselves as having “no particular religion,” were less likely to say that religion was an important part of their lives than eight years ago.The surveyors did not find any evidence that young Americans who are now irreligious will become more so as they age; on the contrary more people of every age group are leaving church than joining.
The ranks of the unaffiliated have been bolstered by former Christians. Nearly a quarter of people who were raised as Christian have left the group, and ex-Christians now represent 19 percent of adults. . . .
Younger adults have been particularly likely to join the unaffiliated in recent years. In 2007, 25 percent of 18-to-26-year-olds were unaffiliated; now 34 percent of the same cohort is unaffiliated.
It is interesting to me that the percentage of Americans who identify as Jewish is unchanged, even though many American Jews are completely secular. To be Jewish is an identity that survives the loss of the religious component, whereas a Christian identity is specifically religious.