William Callahan
William Callahan may refer to:
- William A. Callahan, Canadian political scientist
- William F. Callahan, chairman of the Massachusetts Turnpike Authority
- *Callahan Tunnel or William F. Callahan Tunnel, a Boston Harbor tunnel
- William J. Callahan (Secret Service), Deputy Director of the United States Secret Service
- William J. Callahan, candidate in the 1936 United States Senate election in New Hampshire
- William P. Callahan, American Roman Catholic bishop
- William R. Callahan (priest), American Roman Catholic priest
- William R. Callahan (state representative), Massachusetts state representative
- William Roger Callahan, journalist and politician in Newfoundland, Canada
- Bill Callahan (American football coach), American football coach
- Bill Callahan (defensive back), American football player
- Bill Callahan (musician), American singer-songwriter
- Bill Callahan (TV producer), former producer and writer for ''Scrubs''