Observers point to many reasons for the shifts. People may change churches because they relocate to a part of the country where different denominations predominate, or they may prefer another style of worship. Whatever the reasons, the survey reveals some clear winners and losers.
Protestantism, which has shaped American identity for generations, may soon become a minority faith. In the 1980s, 65 percent of Americans called themselves Protestants; today that number is down to 51 percent. Only 43 percent of those aged 18-29 say they are Protestant.
Much has been written about the declines in mainline churches. But in comparing the current religious affiliation of adults with their childhood affiliations, the survey found a net loss of 3.7 percent for Baptists (Baptists account for one-third of all Protestants and nearly two-thirds of black Protestant churches.)
Perhaps the big surprise, though, relates to Roman Catholicism, which experienced the greatest net loss. While 31.4 percent of adults say they were raised Catholic, today only 23.9 percent identify as Catholic, a net loss of 7.5 percent.
"The Catholic numbers are eye-popping," says Dr. Lugo. "One out of every 10 people you meet on the street is a former Catholic."
Fortunately for the Church, however, its share of the religious pie has remained steady in recent decades, due partly to conversions but largely to immigration. Catholics account for 24 percent of the adult population, but immigration could well boost its future share.
"Within our society, Protestants basically outnumber Catholics 2 to 1," Lugo says. "Among immigrants, it's the reverse: Catholics outnumber Protestants by more than 2 to 1."
The big winner on the shifting religious scene is the group of "unaffiliated" Americans. Today 16.1 percent of adults fit that category. Among young people 18 to 29, one-quarter are unaffiliated.