Wikipedia states his religion as "Christianity" and cites the following references as support for that claim:
^ "American President: Barack Obama". Charlottesville, VA: Miller Center of Public Affairs, University of Virginia. 2009. Archived from the original on January 23, 2009. Retrieved January 23, 2009. "Religion: Christian"
"The Truth about Barack's Faith". Obama for America. Archived from the original on January 5, 2011. Retrieved July 1, 2012.
Miller, Lisa (July 18, 2008). "Finding his faith". Newsweek. Archived from the original on February 6, 2010. Retrieved February 4, 2010. "He is now a Christian, having been baptized in the early 1990s at Trinity United Church of Christ in Chicago."
Barakat, Matthew (November 17, 2008). "Obama's church choice likely to be scrutinized; D.C. churches have started extending invitations to Obama and his family". Associated Press. msnbc.com. Archived from the original on January 24, 2009. Retrieved January 20, 2009. "The United Church of Christ, the denomination from which Obama resigned when he left Wright's church, issued a written invitation to join a UCC denomination in Washington and resume his connections to the church.".
"Barack Obama, long time UCC member, inaugurated forty-fourth U.S. President". United Church of Christ. January 20, 2009. Archived from the original on January 25, 2009. Retrieved January 21, 2009. "Barack Obama, who spent more than 20 years as a UCC member, is the forty-fourth President of the United States."
Sullivan, Amy (June 29, 2009). "The Obama's find a church home—away from home". Time. Retrieved February 5, 2010. "instead of joining a congregation in Washington, D.C., he will follow in George W. Bush's footsteps and make his primary place of worship Evergreen Chapel, the nondenominational church at Camp David.".
Kornblut, Anne E. (February 4, 2010). "Obama's spirituality is largely private, but it's influential, advisers say". The Washington Post. p. A6. Retrieved February 5, 2010. "Obama prays privately ... And when he takes his family to Camp David on the weekends, a Navy chaplain ministers to them, with the daughters attending a form of Sunday school there."
He himself stated:
My family, frankly, they weren't folks who went to church every week. My mother was one of the most spiritual people I knew but she didn't raise me in the church, so I came to my Christian faith later in life and it was because the precepts of Jesus Christ spoke to me in terms of the kind of life that I would want to lead.
Doesn't sound like an atheist...