Millard Fillmore previously served as U.S. Vice-President from 1849-50 under Pres. Taylor.
Millard Fillmore was Unitarian. He joined the Unitarian Church in 1831, nearly two decades before he became President upon the death of Pres. Taylor.
From: Peter Roberts, "Millard Fillmore" page in "God and Country" section of "Science Resources on the Net" website (http://www.geocities.com/peterroberts.geo/Relig-Politics/MFillmore.html; viewed 23 November 2005):
Religious Affiliation: Unitarian
Summary of Religious Views:
Fillmore [originally] had no formal religious ties, and indeed had shown relatively little interest in religion, until he joined the Unitarian church in about 1831.
"In my opinion, Church and State should be separate, not only in form, but fact -- religion and politics should not be mingled." -- from a series of campaign speeches, Summer of 1856