The number of Americans who identify as Christian has fallen nearly eight percentage points in only seven years, according to a new survey.
Pew Research Center found that 71% of Americans identified as Christian in 2014 - down from 78% in 2007.
In the same period, Americans identifying as having no religion grew from 16% to 23%.
Fifty-six million Americans do not observe any religion, the second largest community after Evangelicals.
The United States still remains home to more Christians than any other nation, with roughly seven-in-ten continuing to identify with some branch of Christianity.
In 2007 and then again in 2014, Pew conducted the "Religious Landscape Study", interviewing 35,000 people each time.
Pew researchers say the losses they discovered were driven mainly by a decrease among liberal Protestants and Catholics and occurred in all regions of the US and among all ages and demographics.
About 5 million fewer Americans now identify as Christian compared to when the study was conducted in 2007.
In the South, those not-affiliated with religion - or as the researchers call them, "nones" - rose to 19% of the population, while in the Northeast they climbed to 25%.
In the West "nones" are a larger group than any religion, making up 28% of the public.
Greg Smith, Pew's associate research director, said the findings "point to substantive changes" among the religiously unaffiliated, not just a shift in how people describe themselves.
Non-religious Americans have become increasingly organised since 2007, forming political groups designed to keep religion out of public life.
Kelly Damerow with the Secular Coalition for America tells BBC News that the Pew findings "lend credence to the growth we've witnessed within our community and that we have the potential to hold a lot of political clout".
Christians in the US
Americans who identify as Christian: 70.6%
Protestant faiths: 46.5%
Mainline or liberal: 14.7%
Jehovah's Witness: 0.8%
Identify as Other Christians: 0.4%
Source: Pew Research Center