Wikipedia
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.