CHICAGO -- Counted together, independent evangelical congregations comprise one of the largest religious groups in the nation, after Roman Catholics and their evangelical counterparts in the Southern Baptist Convention.
Meanwhile, Mormons rank as the fastest-growing group in the nation, followed by Muslims.
That's according to the census of American religious congregations unveiled Tuesday.
This year, for the first time, a nationwide aggregation of religious traditions counted nondenominational evangelical congregations, ranging from storefront sanctuaries to megachurches.
The 2010 U.S. Religion Census revealed that evangelicals affiliated with independent churches make up the third-largest religious group in the nation. In fact, in 48 out of 50 states, "sovereign" evangelicals occupy a top five spot. The 2010 U.S. Religion Census also improved upon past years by mapping Buddhists, Hindus, four branches of the Jewish community and practitioners of the primarily Japanese Shinto tradition.
Pennsylvania ranked as the most diverse state in the union with 184 religious bodies.
Religious leaders and sociologists welcomed the overview of America's religious landscape as a helpful tool for determining where to evangelize and understanding where certain religious traditions thrive. But some caution that the numbers and rankings could be skewed in some cases because religious groups apply different standards for counting adherents.
The religious census is the latest in a series of reports released each decade to coincide with figures from the U.S. census. It is compiled by the Association of Statisticians of American Religious Bodies. The 2010 edition is the sixth since the U.S. Census Bureau stopped asking questions about religious affiliation after World War II.
Overall, the study shows a profoundly Christian nation with a lot of variety beneath the surface, including about 150 million Americans -- half the population -- who aren't engaged with a religious community.
To compensate for organizations that count membership differently, the numbers represent "adherents," or members, their children and other participants.
In most cases, numbers are supplied by the headquarters of each denomination, although in a few cases such as the nondenominational and Muslim categories, scholars' surveys were used. The geographical spread reflects where people worship -- not where they live.
Steve Warner, a sociologist of religion at the University of Illinois-Chicago, said the decennial study is the best attempt at mapping religion in America.
"What we get is a geographic distribution about where the heartlands and hinterlands of the religious bodies are. They're not evenly distributed," he said, adding that the Methodists seem to be the exception. "They're everywhere."
Researchers say collecting data from religious groups produces a more meaningful picture than leaving it up to individuals to self-identify, because people who affiliate with institutions tend to hew more closely to religious teachings.
"It's not enough to say to an individual, 'Do you identify with a particular tradition?' That doesn't have much substance and therefore may not have much meaning rather than an idea just floating around in their head," said Scott Thumma, a sociologist of religion at the Hartford Institute for Religion Research. "The real difference comes when someone says that and is connected to a community and is active in the local context. Then you begin to see people who are giving, more willing to reach out to their fellow human beings, more likely to volunteer."
Nationwide, The Church of Jesus Christ of Latter-day Saints, or Mormons, reported the most growth of all religious traditions in the U.S.
The study shows Catholics, though still the largest U.S. denomination, declined about 5 percent nationwide. However, researchers warned that numbers from previous studies were not wholly comparable.
Kamilah Jones, 34, a member of Willow Chicago, said the high ranking of nondenominational churches did not surprise her.
"I do really think there's a surge in the movement of nondenominational evangelical churches largely based on churches that are doing more to be active in the community, active in social justice, and also more multicultural in nature," said Jones, who grew up Catholic. "There's something to be said for 'action speaks louder than words.'aa"