The Deasy family was mainly concentrated in Waterford and West Cork at the time that James Joyce wrote Ulysses. However, the name was already known as the college friend and political ally of Daniel O'Connell, Rickard Deasy, instituted the Deasy Land Act, which was intended to reform tenants' rights. Also Captain Timothy Deasy was one of the prisoners rescued from a prison van in Manchester by Fenians in a famous incident in 1867.
Latter day famous members of the clan include Austin Deasy, who became minister for agriculture from 1982 - 1987.
During the great famine many Deasys left Ireland for a better life elsewhere. Five brothers from a faction of the West Cork Deasys settled in Marlborough Massachusetts USA. The brothers, John,Thomas, Timothy, Patrick and William changed the spelling of their name to Dacey. Today they have many descendants living in New England and as far away as California, Washington state, Texas, and Hawaii.
- Henry Hugh Peter Deasy - (1866-1947) automotive pioneer.
- Conor Deasy - Irish pop band The Thrills singer
- Austin Deasy - Irish politician
- Tim Deasy - English Footballer
- Damien Deasy - League Of Ireland Footballer, UCD / Bohemians F.C.
- John Deasy - Irish politician
- Liam Deasy - Irish Republican Army officer during war of independence
- Bill Deasy - American singer-songwriter, recording artist and author
- Daniel Deasy - Democratic member of the Pennsylvania House of Representatives.
- Timothy Deasy - Captain in the Irish Republican Brotherhood.
- Jeff Deasy - Founder of .
- Derek Deasy - AKA Delboy Deasy...Legend
- Brian W Deasy - Retired Denver Police Sergeant/ Veteran of Vietnam War
- Daniel N Deasy - Family Law Attorney
- Timothy E Deasy - Private Investigator, Colorado/ Veteran of Iraq War
- Matthew R.D. Deasy - Indian High Jumper
- Oliver J.R. Deasy - Hockey player, entrepreneur
- Hannah E.M. Deasy - Soprano, Wedding Singer
- Jamie Deasy - Park Celtic u15 top scorer with record breaking 146 goals
- Mike Deasy - Prolific live and session guitarist, member of The Wrecking Crew
- Michael Deasy (born 1977), Irish footballer