Fewer than half of American adults define themselves as Protestant, marking the first time the faith group has decreased significantly below 50 percent, according to a new study from the Pew Research Center’s Forum on Religion & Public Life.

While the Protestant portion of the population has declined, the number of Americans who do not identify with any religion -- also known as “nones” -- is rising, the study shows.

One-in-five adults -- about 46 million -- have no religious affiliation: That group includes more than 13 million atheists and agnostics and nearly 33 million adults who describe themselves as having no particular religious affiliation.

Here’s more from Pew detailing the results of the study:

The growth in the number of religiously unaffiliated Americans “is largely driven by generational replacement, the gradual supplanting of older generations by newer ones. A third of adults under 30 have no religious affiliation (32%), compared with just one-in-ten among those who are 65 and older (9%). And young adults today are much more likely to be unaffiliated than previous generations were at a similar stage in their lives.”

“In 2007, 53% of adults in Pew Research Center surveys described themselves as Protestant. In multiple surveys conducted in the first half of 2012, fewer than half of American adults say they are Protestant (48%). This marks the first time in Pew Research Center surveys that the Protestant share of the population has dipped significantly below 50%. The decline is concentrated among white Protestants, including those who consider themselves born-again or evangelical Protestants as well as those who do not.”

To read the full study, check out http://www.pewforum.org/