William Simon Duffey Jr. (born 1952) is a United States federal judge.
Born in Philadelphia, Pennsylvania, Duffey received a B.A. from Drake University in 1973 and a J.D. from the University of South Carolina Law School in 1977. He was a Private practice from 1977 to 1978. He was an Assistant staff judge advocate, U.S. Air Force from 1978 to 1981. He was in private practice in Atlanta, Georgia from 1981 to 2001. He was a Deputy and associate independent counsel, Office of Independent Counsel - Whitewater from 1994 to 1995. He was an Adjunct professor, University of South Carolina in 2000. He was the United States Attorney for the Northern District of Georgia from 2001 to 2004.
Duffey was a federal judge on the United States District Court for the Northern District of Georgia. Duffey was nominated by President George W. Bush on November 5, 2003, to a seat vacated by J. Owen Forrester. He was confirmed by the United States Senate on June 16, 2004, and received his commission on July 1, 2004.