William Hennessy
William Hennessy may refer to:
- Bill Hennessy (Cork hurler)
- Bill Hennessy (Kilkenny hurler)
- William Hennessy (violinist), Australian classical violinist
- William C. Hennessy, American civil servant and political figure
- William J. Hennessy Jr., American court sketch artist
- William John Hennessy, Irish artist
- William Maunsell Hennessy, Irish official and scholar