For the first time since researchers began tracking the religious identity of Americans, fewer than half said they were Protestants, a steep decline from 40 years ago when Protestant churches claimed the loyalty of more than two-thirds of the population.

A new study released on Tuesday by the Pew Forum on Religion and Public Life found that it was not just liberal mainline Protestants, like Methodists or Episcopalians, who abandoned their faith, but also more conservative evangelical and “born again” Protestants. The losses were among white Protestants, but not among black or minority Protestants, the study found, based on surveys conducted during the summer.

When they leave, instead of switching churches, they join the growing ranks who do not identify with any religion. Nearly one in five Americans say they are atheist, agnostic or “nothing in particular.”

This is a significant jump from only five years ago, when adults who claimed “no religion” made up about 15 percent of the population. It is a seismic shift from 40 years ago, when about 7 percent of American adults said they had no religious affiliation.