Stetzer points to what he calls the “Willowback phenomenon” as a cause. Thousands of churches now follow the methods of two super-size megachurches — Willow Creek Community Church in Barrington, Ill., and Saddleback Church in Lake Forest, Calif. Both stress contemporary music and sermons and services that make the unchurched feel at ease. Both downplay doctrines and denominational differences

Pete Wilson likes Baptists.

In fact, he used to be one.

But when he launched interdenominational Crosspoint Church 10 years ago, Wilson dropped his Baptist ties. He believes what Baptists believe, and he appreciates the mission work they do. He just doesn’t see the personal benefit to being part of any denomination.

“It just seemed like a lot of meetings and a lot of talk,” Wilson said.

At the same time mainstream denominations lose thousands of members per year, churches such as Crosspoint are growing rapidly — 15 percent of all U.S. churches identified themselves as nondenominational this year, up from 5 percent a decade ago. A third dropped out of major denominations at some point.

Their members are attracted by worship style, particular church missions or friends in the congregation.

“They no longer see the denomination as anything that has relevance to them,” said Scott Thumma, a religion sociology professor at Hartford Seminary in Hartford, Conn. He’s compiling a list of nondenominational churches for the 2010 Religious Congregations and Membership Study. “The whole complexion of organized religion is in flux.”

Denominations share theological, organizational and legal ties. They send out missionaries; build colleges, seminaries and hospitals; and fund pension plans for pastors.