John Dempsey may refer to:
- John Dempsey (footballer) (born 1946), Irish retired footballer
- John Dempsey (lyricist), also playwright
- John Dempsey (Medal of Honor recipient) (1848–?), American sailor and Medal of Honor recipient
- John N. Dempsey (1915–1989), American politician, governor of Connecticut
- John J. Dempsey (1879–1958), American politician, governor of New Mexico
- John Dempsey (cartoonist), American single-panel cartoonist
- John Dempsey (novelist) (fl. c. 1990s)