One in five Americans -- and one in three of adults under 30 -- is religiously unaffiliated, the highest percentage ever, according to a Pew Research Center study released Tuesday.

Over the past five years, the study found, the number of religiously unaffiliated adults has increased from slightly over 15 percent to just under 20 percent, a figure that includes more than 13 million self-described atheists and agnostics, as well as almost 33 million adults who do not identify themselves with a particular religion.

Survey takers were able to choose from a list that included more than a dozen possible affiliations, including “Catholic,” “Protestant,” "Orthodox," “don't know” and “nothing in particular.”

But, according to the nationwide survey, many of the 46 million unaffiliated adults or so-called "nones" are spiritual or religious in some way:

• 68 percent say they believe in God.
• 58 percent say they feel a connection with nature and the Earth.
• 37 percent say they think of themselves as "spiritual" but not "religious."
• 21 percent say they pray daily.

Most "nones" said religious institutions can benefit communities through their social outreach, but an overwhelming majority thinks religious organizations are too focused on rules, money and power and too involved in politics.

Pew says the rise of the religiously unaffiliated is mainly due to a generational shift, with 32 percent of adults under 30 saying they're religiously unaffiliated, compared with only 9 percent of those aged 65 and older.

Politically, the "nones" skew heavily toward the Democratic Party, making up 24 percent of the Democratic and Democratic-leaning registered voters, the largest religious constituency. Black Protestants at 16 percent, white mainline Protestants at 14 percent and white Catholics at 13 percent are some of the other large religious groups skewing Democratic.

With social issues such as same-sex marriage taking center stage this election season, 73 percent of "nones" say they support gay marriage and 72 percent support legal abortion.

According to Pew, a counterpoint to the rise of the religiously unaffiliated has been a dip in the share of the population that identifies as Protestant. That figure now stands at 48 percent, down from 53 percent in 2007. It is the first time the number of Protestants has fallen significantly below 50 percent, according to Pew. This is a continuation of a long-term trend, as the Protestant population has been declining since the early 1990s.   

The number of Catholics, which now stands at 22 percent, has been steady for a few years, the study shows, owing in part to immigration from Latin America.

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