A Thomas Churchill emigrated to St. Louis Mo from Tipperary and was born about 1826, the same year you mention Samuel Churchill had a son Thomas. This Thomas Churchill was 25 years old upon arrival Dec. 5, 1851 on the ship William D. Sewall out of Liverpool England according to the ship's list. He debarked in New Orleans, Louisana. He was listed as a tailor. He was married (Ireland or Missouri?) and had about eight children, four of whom died before reaching adulthood. He died in 1878.
Not sure how or if this any of this fits in with the Canadian Samuel Churchill of Tipperary. Could Samuel have later returned to Thurles in Tipperary from Canada?