“It’s remarkably widespread,” said Alan Cooperman, director of religion research for the Pew Research Center. “The country is becoming less religious as a whole, and it’s happening across the board.”

At the same time, the share of those who are not affiliated with a religion has jumped from 16 percent to about 23 percent in the same time period. The trend follows a pattern found earlier in the American Religious Identification Survey, which found that in 1990, 86 percent of American adults identified as Christians, compared with 76 percent in 2008.

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Here are three key takeaways from Pew’s new survey.

1. Millennials are growing even less affiliated with religion as they get older

The older generation of millennials (those who were born from 1981 to 1989) are becoming even less affiliated with religion than they were about a decade ago, the survey suggests. In 2007, when the Pew Research Center did their last Religious Landscape Survey and these adults were just entering adulthood, 25 percent of them did not affiliate with a religion, but this grew to 34 percent in the latest survey.

The trends among the aging millennials is especially significant, said Greg Smith, associate director of research at the Pew Research Center. In 2010, 13 percent of baby boomers were religiously unaffiliated as they were entering retirement, the same percentage in 1972.

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“Some have asked, ‘Might they become more religiously affiliated as they get older?’ There’s nothing in this data to suggest that’s what’s happening,” he said. Millennials get married later than older generations, but they are not necessarily more likely to become religiously affiliated, he said.

2. There are more religiously unaffiliated Americans than Catholic Americans or mainline Protestant Americans

The numbers of Catholics and Protestants have each shrunk between three and five percentage points since 2007. The evangelical share of the American population has dropped by one percentage point since 2007.

There are more religiously unaffiliated Americans (23 percent) than Catholics (21 percent) and mainline Protestants (15 percent). “That’s a striking and important note,” Smith said.

The groups experience their losses through what’s called “religious switching,” when someone switches from one faith to another. Thirteen percent of Americans were raised Catholic but are no longer Catholic, compared with just 2 percent of Americans who are converts to Catholicism.

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“That means that there are more than six former Catholics for every convert to Catholicism,” Smith said. “There’s no other group in the survey that has that ratio of loss due to religious switching.”

There are 3 million fewer Catholics today than there were in 2007. While the percentage of Catholics in the United States has remained relatively steady, Smith said we might be observing the beginning of the decline of the Catholic share of the population.

Pew estimates there are about 5 million fewer mainline Protestants than there were in 2007. About 10 percent of the U.S. population say they were raised in the mainline Protestant tradition, while 6 percent have converted to mainline Protestantism.

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Evangelical Protestants have experienced less decline, due to their net positive retention rate. For every person who has left evangelical Protestantism after growing up, 1.2 have switched to join an evangelical denomination.

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3. Those who are unaffiliated are becoming more secular

The “nones,” or religiously unaffiliated, include atheists, agnostics and those who say they believe in “nothing in particular.” Of those who are unaffiliated, 31 percent describe themselves as atheists or agnostics, up six points from 2007.

“What we’re seeing now is that the share of people who say religion is important to them is declining,” Smith said. “The religiously unaffiliated are not just growing, but as they grow, they are becoming more secular.”

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And people in older generations are increasingly disavowing organized religion. Among baby boomers, 17 percent identify as a religious “none,” up from 14 percent in 2007.

“There’s a continuing religious disaffiliation among older cohorts. That is really striking,” Smith said. “I continue to be struck by the pace at which the unaffiliated are growing.”

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White Americans (24 percent) are more likely to say they have no religion, compared with 20 percent of Hispanic Americans and 18 percent of black Americans. The retention rates of the “nones” who say they were raised as religiously affiliated has grown by seven points since 2007 to 53 percent.

The Pew survey was conducted between June and September of 2014.