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Ancient History of the Dempsey Clan in Ireland


The Irish people are famous for their poets, scholars, playwrights, authors, artists and statesmen. Evidence of the age of Irish culture is exemplified by the oldest standing building in the world, and many pieces of fine jewellery predating biblical times.

Researchers have concluded that the family name Dempsey was first found in King's county where they had been seated from early times. This brief history of the Dempsey family was compiled using books by O'Hart, McLysaght and O'Brien, and Woulfe, baptismals, parish records, and ancient land grants.

The surname, Dempsey, occurrs in many references, but from time to time, was recorded as Dempsey, O'Dempsey, Dempsy, Dempsay, Dempsie, and these changes in spelling frequently occurred within the same family. It was not uncommon for a person to be born with one spelling, married with another, and have yet another at his wake.

The ancient Kings of Ireland were descended from King Milesius of Spain, the grandson of Breoghan, (or Brian) King of Galicia, Andalusia, Murcia, Castile and Portugal. Milesius sent his uncle northward from Spain with his own son Lughaidh to explore the western Isles. This was said to have fulfilled an ancient Druidic prophecy.

Upon learning that his son had been murdered by the three resident Irish Kings (the Danans) in Ireland, King Milesius gathered an army to take his revenge on the Irish. Although he died before embarking on the trip, his eight surviving sons succeeded in conquering Ireland.

The Dempsey name emerged in King's county. Dempsey is the anglicized version of O'Dempsey the ancestor of O'Diomasaighe. This family name came in turn from the Irish word "diomusach" meaning proud, haughty, or arrogant. The Dempseys were also associated with the second century Irish King, Cathair Mor.

The Dempsey territory included territory on both sides of the River Barrow in the King's and Queen's counties. Their extensive holdings also included parts of the baronies in King's county, Queen's county and part of Offaly in the county of Kildare.

A significant event occurred in the history of Ireland and the Dempsey family in 1172. The King of Leinster asked the Earl of Pembroke, commonly known as Strongbow, to assist in securing the Kingship of Ireland. What resulted was nothing less than an Anglo-Norman invasion of Ireland.


O'Dempsey, Chief of Offaly, was one of the few Irish leaders who could boast of having defeated Strongbow in military engagement. Strongbow's son-in-law, de Quencl, was killed in the battle. Later Dermot O'Dempsey (d. 1193), Chief of the Name, founded the Cistercian Abbey at Monasterevin near Portarlington. The Dempseys switched their allegiances and were sometimes loyal to the Stuart royalty. In fact, James I bestowed upon one clan member the title Viscount Clanmalier, the family then being, in the reign of Elizabeth I, consistently pro-English.

Later on in the seventeenth century the O'Dempseys took the Irish side. Edmond O'Dempsey, Bishop of Leighlin, Lewis O'Dempsey, Viscount of Kilkenny, and Barnabas O'Dempsey, were prominent members of the confederation of Kilkenny, and, with Lysagh O'Dempsey, were exempted from pardon by the Cromwellian victors in 1652. Their loyalty to the Catholic King James resulted in the loss of their estates.

The O'Dempseys were now faced with a challenge. To many the long history of the family name could not free them from the strong bonds holding them to Ireland and to the loyal clan members. They remained on the borders of Leinster and Offaly. Notable amongst the family name at this time was O'Dempsey of King's county.

During the 12th century, 1172 AD, Dermott McMurrough, King of Leinster, requested King Henry II of England for assistance. This was the first intrusion into Ireland of the Anglo/Normans. Many native Irish families lost their lands and possessions. This invasion was followed by Cromwell's invasion of 1640, when further loss of land befell the unfortunate Irish people.

In 1845, the great potato famine caused widespread poverty. Many Irish joined the armada of sailing ships which sailed from Belfast, Dublin, Cork, Holyhead, Liverpool, and Glasgow, all bound for the New World. Some called these ships the "White Sails." Others called them "Coffin Ships," since nearly 25% of the passengers died of disease and were buried at sea.

In North America, some of the first migrants who could be considered kinsmen of the Dempsey family were Edward Dempsey who settled in New York in 1810, Jeremiah Dempsey who settled in Mississippi in 1820, and Edward Dempsey settled in Boston, Massachusetts, in 1849. Ann, Biddy, Bridget, Catherine, John, and Henry Dempsey settled in Quebec in 1840.

Some Dempseys remained loyal to the British Crown during the American War of Independence, and were forced to move to Canada, becoming known as the United Empire Loyalists. Meanwhile, the family name Dempsey produced many prominent people, including heavywight boxing champion Jack Dempsey, and James Dempsy, President of General Dynamics Corp. among many others.

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