Jefferson was a Unitarian. If that makes him a non-Christian, then John Adams, Abigail Adams, John Quincy Adams, Millard Filmore, Daniel Webster and Julia Ward Howe (writer of the lyrics to the Battle Hymn of the Republic), who were also Unitarians, were not Christians either.
A refutation of the charge that Unitarians were not Christian was best answered in William Ellery Channing's 1819 Unitarian Christianity, or The Baltimore Sermon