William F. Downes (born 1946) is a retired United States federal judge.
Born in Boston, Massachusetts, Downes received a B.A. from the University of North Texas in 1968 and served in the U.S. Marine Corps from 1968 to 1971. He received a J.D. from the University of Houston Law Center in 1974. He was in private practice in Green River, Wyoming from 1975 to 1978 and in Casper, Wyoming from 1978 to 1994.
On May 5, 1994, Downes was nominated by President Bill Clinton to a new seat on the United States District Court for the District of Wyoming created by 104 Stat. 5089. He was confirmed by the United States Senate on June 15, 1994, and received his commission on June 16, 1994. He became chief judge in 1999 and retired in 2011.