A growing minority of Americans refuses to identify with traditional religion, a trend particularly strong among young adults, while self-identified Catholics and more liberal Protestants are declining as shares of the population.

That’s according to a massive survey released today by the Pew Research Center of more than 35,000 Americans, an unusually large sample with a margin of error of less than a percentage point.

The poll confirms what Pew and several other polling firms have found since at least the turn of the century — a growing minority of “nones,” or Americans who choose none-of-the-above from a menu of religious affiliations.

The unaffiliated are nearly 23 percent of the population, up from 16 percent in 2007, the last time Pew did a similarly vast survey. They include atheists and agnostics, 7 percent, and those who say they’re “nothing in particular,” 16 percent, some of whom are thoroughly secular and others of whom practice a do-it-yourself spirituality.

“We’ve known it (the unaffiliated population) has been growing for a couple decades,” said Greg Smith, lead researcher for the report. “The pace it continues to grow is very striking.”

There are plenty of caveats.

The United States still has the world’s largest Christian population at an estimated 173 million.

Evangelicals, 25 percent of the population, and historically black Protestant groups, 7 percent, are roughly holding their numbers, and independent churches are picking up some of the slack from declining Protestant denominations. Immigration is fueling growth of small groups such as Muslims, Hindus and Jehovah’s Witnesses.

Whether Americans have a religion or not, they are more likely to think it unimportant now, 22 percent, than they did seven years ago, 16 percent.