William Duffy Keller (born 1934) is a United States federal judge.
Born in Los Angeles, California, Keller received a B.S. from the University of California, Berkeley in 1956 and an LL.B. from the University of California, Los Angeles, School of Law in 1960. He was an assistant U.S. Attorney of the Southern District of California from 1961 to 1964. He was in private practice in California from 1964 to 1972. He was the United States Attorney for the Central District of California from 1972 to 1977. He was in private practice in California from 1977 to 1984.
Keller was a federal judge on the United States District Court for the Central District of California. Keller was nominated by President Ronald Reagan on September 11, 1984, to a new seat created by 98 Stat. 333. He was confirmed by the United States Senate on October 3, 1984, and received his commission on October 4, 1984. He assumed senior status on October 29, 1999.