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For other uses, see Dempsey (disambiguation).

Dempsey is a surname of Irish origin.


Dempsey is an anglicised form of Ó Diomasaigh, « descendant of Díomasaigh »; the latter stems from the Irish adjective díomasach « proud ».[1] The family originated in the Kingdom of Uí Failghe.

According to John Grenham:

"In the original Irish Dempsey is Ó Diomasaigh, from diomasach, meaning "proud". The name was also occasionally anglicised "Proudman". The Ó Diomasaigh originated in the territory of Clanmalier, on the borders of what are now counties Laois and Offaly, and remained powerful in the area until the seventeenth century. In the 12th century. O’Dempsey, Chief of Offaly, was one of the few native Irish leaders who defeated Strongbow. In later years, their allegiance was to the English and they were involved with the newcomers in the massacre of the O’Lalors in Laois in 1577, an action which local tradition says was responsible for their later losses. James I recognised the strength of the family by granting the title "Viscount Clanmalier" to Terence Dempsey. The loyalty of the family to the Crown was short-lived, however, and the Williamite wars later in the century destroyed their power and scattered them." [1]

Another source states:

"The O'Dempsey family derive their name from Diummasach, an 11th-century Uí Failge prince of the Clann Máel Ugra, aka Cenél Maoilughra. The Clann Máel Úgra, in turn, took their name from Máelaugrai, an Uí Failge chieftain who flourished in the middle of the 9th century. The center of their territory, anglicized Clanmalier, was near Ballybrittas in northeast Co. Leix. Their power later extended into the barony of Upper Phillipstown. O'Donovan, in his Ordnance Survey letters, places Clann-Maoilughra in the present Barony of Upper Philipstown in the King's County and the Barony of Portnahinch in the Queen's County." [2]

The family of the viscounts Clanmalier were attainted upon the death of Maximilian, the 3rd viscount, in 1691.


An Ó Diomasaigh genealogy records the following:

Flann m. Máel Ruanaid m. Cellaich m. Máel Augra m. Conchobuir m. Áeda m. Tomaltaich m. Flaind m. Díumasaich m. Congaile m. Forannáin m. Congaile m. Máel h-Umai m. Cathail m. Bruidge m. Nath Í m. Rosa Failgi. [3]

The final person may be identical with Failge Berraide (fl.507-514), a King of the Uí Failge and of Laigin descent (see List of kings of Uí Failghe).

Dempseys in the annals[edit]

The Irish annals list a number of members of the family:

  • 789: Áedh [grandfather of Máelaugrai] was slain by Óengus son of Mugrón, king of Uí Failge, in the oratory of Kilclonfert.
  • 1141: Donnchadh, son of Goll Gaibhle, i.e. Ua Conchobhair Failghe, was killed by the Ui-Failghe themselves, i.e. the Clann-Maelughra.
  • 1161: Domhnall, son of Conghalach, son of Cuaifne Ua Conchobhair Failghe, Tanist of Ui-Failghe, was slain by the Clann-Maelughra.
  • 1164: Maelseachlainn Ua Conchobhair Failghe, was slain by the Clann-Maelughra.
  • 1193: Diarmait, son of Cubrogam Ua Diumasaigh, chief of Clann-Mailighra and king of Ui-Failghe for a long time, died.
  • 1383: Dermot O'Dempsy, Lord of Kinel-Maoilughra, was slain by the English.
  • 1394: Thomas O'Dempsy, heir to the lordship of Clann-Maoilughra, was slain by the English.

Other Dempsey families[edit]

An unrelated family, Mac Diomasaigh, are found in County Antrim and its neighbouring counties [4].

Bearers of the name[edit]

The name Dempsey may refer to:



As a given name:

External links[edit]


  1. ^ P.H. Reany & R. M. Wilson, A dictionary of English Surnames, Oxford University Press, Oxford, 3rd ed., 1995, p. 131a; Edward MacLynsaght, The Surnames of Ireland, Irish Academic Press, 6th ed., Dublin, 1991, p. 79.