De Lee, a Unitarian Universalist, grew up in rural Kansas, where members of his faith were few and far between. Attending services meant an overnight trip to Kansas City, Mo., where the nearest Unitarian Universalist congregation was.

Today, getting to church is easy for De Lee, an astronomer at Vanderbilt University. He’s a regular in the choir on Sundays at First Unitarian Universalist Church in Nashville, which has a congregation of about 500.

De Lee is one of a growing number of Unitarian Universalists, a group of people who believe in organized religion but are skeptical about doctrine. The denomination grew nationally by 15.8 percent from 2000 to 2010, according to the Association of Statisticians of American Religious Bodies.

Although they remain small in total numbers with about 211,000 adherents nationwide, Unitarians believe their open-minded faith has a bright future as an alternative to more exclusive brands of religion.

They might be right, said Diana Butler Bass, author of “Christianity After Religion: The End of Church and the Birth of a New Spiritual Awakening.” Bass, who has studied thriving progressive churches, said Unitarian Universalists can fill a niche in conservative religious cultures such as the Bible Belt.