- William Jacob Morgan
- William James Adams Jr.
- William James Edwards Lee III
- William James Kirkpatrick
- William James Ross
- William Janiak
- William Jay Smith
- William Jeffrey
- William Jennings Bryan
- William Jessup University Alumni & Community Choir
- William Jimenez
- William Johann Rodriguez
- William Johansson
- William John Meng
- William Johnson
- William Johnson
- William Johnson
- William Johnstone
- William Joseph
- William Joseph Watkins
- William Joyner
- William 'JuJu' House
- William June Brown
- William K. "Billy" Hadnott
- William Kahakalau
- William Kane
- William Kanengiser
- William Kapell
- William Katt
- William Katt
- William Katz
- William Kealoha
- William Keihn
- William Kendall
- William Kendall
- William Kennedy
- William Kent
- William Kersten
- William Kersten
- William Kiernan Presents
- William Kimber