James Monroe attended St. John's Episcopal Church while he was President. Some sources classify Monroe was a deist.
From: Peter Roberts, "James Monroe" page in "God and Country" section of "Science Resources on the Net" website (http://www.geocities.com/peterroberts.geo/Relig-Politics/STAgnew.html; viewed 29 November 2005):
Religious Affiliation: Episcopalian
Summary of Religious Views:
Franklin Steiner, in his book The Religious Beliefs of Our Presidents, categorized Monroe among "Presidents Whose Religious Views Are Doubtful." Indeed, Monroe was very close-mouthed about his religious views -- almost nothing on that subject can be found in his speeches or writings.
...James Monroe left almost no documents or speeches pertaining to religion...