William Thomas Hart (born 1929) is a United States federal judge.
Born in Joliet, Illinois, Hart received a J.D. from Loyola University Chicago School of Law in 1951. He was in the United States Army from 1951 to 1953. He was an assistant U.S. Attorney of the Northern District of Illinois from 1954 to 1956. He was in private practice in Chicago, Illinois from 1956 to 1982. He was a Special assistant state attorney general of Illinois from 1957 to 1958. He was a Special assistant state's attorney of Cook County, Illinois in 1960.
Hart was a federal judge on the United States District Court for the Northern District of Illinois. Hart was nominated by President Ronald Reagan on March 11, 1982, to a seat vacated by John Powers Crowley. He was confirmed by the United States Senate on April 20, 1982, and received his commission on April 21, 1982. He assumed senior status on June 1, 1996.