William Willoughby
William Willoughby may refer to:
- William Willoughby, 11th Baron Willoughby de Eresby, father of Katherine Willoughby and the largest landowner in Lincolnshire, England
- William Willoughby, 1st Baron Willoughby of Parham, English baron and nephew of the above
- William Willoughby (c.1566-1615), MP for Nottingham
- William Willoughby, 3rd Baron Willoughby of Parham, English peer
- William Willoughby, 6th Baron Willoughby of Parham, English landowner and politician
- William Willoughby, 5th Baron Willoughby de Eresby, English baron
- William Arnson Willoughby, Ontario physician and political figure
- William F. Willoughby, author of public administration texts
- Bill Willoughby, American former basketball player