https://www.pewforum.org/2019/10/17/in-u-s-decline-of-christianity-continues-at-rapid-pace/
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https://www.prri.org/research/american-religious-landscape-christian-religiously-unaffiliated/
The rise of the Religiously Unaffiliated
The religiously unaffiliated—those who identify as “atheist,” “agnostic,” or “nothing in particular”—now account for nearly one-quarter (24%) of Americans. Since the early 1990s, this group has roughly tripled in size.
Growth of the Religiously Unaffiliated, 1976-2016Line chart with 29 data points.
View as data table, Growth of the Religiously Unaffiliated, 1976-2016The chart has 1 X axis displaying Sources: General Social Survey, 1976-2012; PRRI 2013-2016 Americans Values Atlas.. Range: 1975.6 to 2016.4.The chart has 1 Y axis displaying Values. Range: 0 to 30.Sources: General Social Survey, 1976-2012; PRRI 2013-2016 Americans Values Atlas.ValuesGrowth of the Religiously Unaffiliated, 1976-2016Percent of population198019851990199520002005201020150102030PRRIEnd of interactive chart.
Religious identity is highly stratified by age, with younger Americans (age 18-29) most likely to be religiously unaffiliated and seniors (age 65 or older) least likely to identify this way.
However, the relationship between age and unaffiliated status is not completely linear. While there is considerable variation at the youngest and oldest ends of the age spectrum, there is less variation in the rate of unaffiliated identity among Americans in their 40s (23%), 50s (18%), and 60s (16%).
Although unaffiliated Americans tend to be younger than religiously affiliated Americans on average, the group collectively is older today than it was a generation ago. Today, about one-third (34%) of unaffiliated Americans are under the age of 30, while nearly three in ten (29%) are at least 50 years old. In the 1970s, half (50%) of all unaffiliated Americans were under 30 years old, and only 17% were age 50 or older. The median age of someone who was unaffiliated during that decade was also seven years younger than it is today: 29 vs. 36, respectively.
Atheists, Agnostics, Seculars, and the Religiously Unattached
There are notable differences among the unaffiliated in terms of their religious identity. Only about one-quarter of the unaffiliated identify as atheist (14%) or agnostic (13%), while fewer than one in five (16%) identifies as a “religious person.” The majority (58%) of Americans who are not religiously affiliated do not identify as a religious person.18