New England, where the Puritans and others sought religious freedom, has surpassed the West Coast as the least religious region in America, according to a new major national survey.

The study, released last week, showed that since 1990, the percentage of Americans claiming no religion has nearly doubled, growing to 15% last year. That was the overall conclusion. But tucked inside the report are figures offering portraits of various regions.

Nonbelievers, skeptics and the unaffiliated are clustered in New England and along the Pacific, even as all 48 states surveyed have become less religious, the American Religious Identification Survey found.

On the West Coast, 20% of residents identified with no religion last year, compared with 22% of New Englanders.

Whereas Pacific states have long been called the “unchurched belt,” the irreligious population over the last two decades grew more in New England — where it nearly tripled — than in any other region.

To account for the rise of “Nones” in the six-state region, researchers with the survey point to the area’s shrinking Catholic population: New England is now 36% Catholic, down from 50% in 1990.

“There’s a complete reciprocal, a correlation of Catholics to no religion,” said the survey’s principal investigator, sociologist Barry A. Kosmin of Trinity College in Connecticut.

Survey respondents were not asked whether they left the Catholic Church, but Kosmin and religion scholars said Catholics may feel disaffected with religious institutions in general or estranged by clergy sex abuse scandals.

“The obvious suspect here . . . would be the pedophilia scandals in the Catholic Church,” said Randall Balmer, a professor of American religious history at Barnard College and Columbia University. “In New England, particularly Massachusetts, that hit pretty hard.” Indeed, Massachusetts saw its Catholic population drop 15 percentage points and its unaffiliated group jump 14 percentage points between 1990 and 2008.

But outside New England, 13 states, primarily in the Sun Belt, saw upticks in their Catholic population.

In California, Catholics climbed 8 percentage points and are now the largest religious group in the state at 37% of the population.

In Texas, Catholics grew 9 percentage points to total 32% of the state. However, they are still outnumbered by other Christian denominations, which account for 48% of the population even after falling 20 percentage points.

That Catholics are gaining parishioners in these states is no surprise, scholars said. Latin American immigrants, most of whom are Catholic, have kept the percentage of the nation’s Catholics nearly level: Catholics make up 25% of the country, compared with 26% in 1990, despite adding 11 million adherents.

“While the Catholic Church is holding its own overall numerically, it really has a significant leakage from what you might call the old European stock Catholics. It’s being replenished by immigrants, primarily from Latin America,” said Peter W. Williams, a professor of comparative religion at Miami University in Ohio.

The country’s Latino population has more than doubled since 1990 — from 22.4 million to 45.5 million in 2007 — and is concentrated in border states. In 2007, 48% lived in California or Texas.

But determining the nation’s Catholic population is not as simple as counting the Latino population, said Timothy Matovina, director of the Cushwa Center for the Study of American Catholicism at the University of Notre Dame.

Though the number of Latinos in the country is increasing, many Latino Catholics are switching to Protestant denominations or becoming unaffiliated, Matovina said. And, he said, the percentage of American Latinos who are Catholic falls after the first generation.

“For Latino Catholics, it’s a kind of ‘shrink while you’re growing’ phenomenon,” he said.

The same is true for Christian groups overall, the survey found. Christian denominations added 22 million members since 1990 to total more than 173 million in 2008, but as a proportion of the population, Christians fell from 86% to 76%.

It’s difficult to pin why Americans are abandoning their organized religions in any given region, Matovina said.

“People tend to judge by what happens at 11 o’clock Sunday morning,” he said. “People think much more locally.”

Geographic and social mobility within the country also blur the borders of America’s religious landscape, scholars said. But regional religious distinctions won’t fade entirely, Williams said.

“Regions are like denominations. . . . They tend to shift,” he said. “On the other hand, there are certain basic structures in American life, like religious denominations and regional identity, that are very durable and aren’t static and aren’t going away any time soon.”

The survey can be found at www.americanreligionsurvey-aris.org.