William Duffy

William Duffy, Bill Duffy or Billy Duffy may refer to:
 * Bill Duffy (basketball), American basketball player and player agent
 * Bill Duffy (sportsman) (1866–1959), Australian sportsman
 * Billy Duffy (born 1961), English musician
 * Billy Duffy (hurler) (1931–2005), Irish hurler
 * William Duffy, a pseudonym of William Dufris (1958–2020), an American voice actor
 * William Duffy (bishop), English Roman Catholic bishop
 * William Duffy (politician) (1865–1945), Irish nationalist politician
 * William James Duffy (1888–1946), Canadian politician
 * William J. Duffy (1916–2013), American jurist and legislator