The Pew Forum has a chart listing the religious affiliation of U.S. presidents. Episcopalians are the largest group, way above their proportion in the general population. Presbyterians also are over-represented.

Unitarians also are present in numbers far above their share of the population, though none more recent than Taft. Unitarians are the only non-Christian group present, denying the Trinity and the Divinity of Christ.

Andrew Johnson was our last president without a formal religious affiliation, sharing that category with Abraham Lincoln and Thomas Jefferson. I am not sure that we would elect someone without church membership to the White House today.

For what it's worth, Bill Clinton and Warren Harding both were/are Baptists.

I am not sure that Andrew Jackson is in the correct category. If I get ambitious tonight I'll try to check on it. UPDATE: According to Robert Remini Jackson's people were Presbyterian. He himself united with the Hermitage Presbyterian Church in 1838, after the White House. Had he been baptized as an infant? Remini does not say.