John C. Calhoun was raised in a devout Presbyterian home. Calhoun's family built the landmark Old Stone Church in Clemson, South Carolina, a Presbyterian church.
As numerous biographies and history books attest, John C. Calhoun became a Unitarian as an adult. See, for example, the Pulitzer Prize-winning book John C. Calhoun: American Portrait, by Margaret Coit (p. 508). Also: John C. Calhoun and the Price of Union, by John Niven (p. 104). In 1822, Calhoun was among the 17 founders of the All Souls Unitarian Church in Washington, DC. This church is still a "flagship church" of the Unitarian Universalist Association today.
Although "famous Unitarian" lists are common and frequently include even politicians with only peripheral or nominal association with Unitarian churches or beliefs, it is common for Calhoun to be omitted from such lists because contemporary Unitarian Universalists disapprove of what Calhoun is known for most: his defense of slavery.
From: Peter Roberts, "John C. Calhoun" page in "God and Country" section of "Science Resources on the Net" website (http://www.geocities.com/peterroberts.geo/Relig-Politics/JCCalhoun.html; viewed 23 November 2005):
Religious Affiliation: Unitarian?
Summary of Religious Views:
Calhoun was raised in a strongly Presbyterian household. Always deeply interested in religion, he was quite learned in the subject. Although he never joined a church, and refused to profess himself a Christian, he frequently attended church, particularly the Episcopal church to which his wife belonged. He contributed money to the construction (and is listed as a founding member) of the First Unitarian Church of Washington (which later became All Souls Church), and, for a time, at least, seemed to favor that group. According to one biographer, in matters of religion, "Even his friends had no idea where he stood." (Margaret L. Coit, John C. Calhoun: American Portrait, p. 508)
When Calhoun was on his deathbed, he turned away the Senate chaplain, who had come intending to minister to him.
A Unitarian Universalist website includes the following notes: "...Calhoun was one of the founders of All Souls Unitarian Church (established 1822) in Washington, D.C. He contributed generously to the cost of the church's construction and attended services there. His family, however, was not similarly inclined; his mother-in-law remained a devout Presbyterian and his Episcopalian wife would not attend services at the new Unitarian Church although it was just a few blocks from their home. Calhoun's religion was largely a private matter, one rarely referred to in his writings or public utterances."