Often spelt without the prefix "Mac", the name has many variants, including Gehegan, Geoghan, Geohegan, Gahagan, Gagan, and Gagon which approximate the most common pronunciations of the name. It is usually pronounced gay-gan, ge-heg-an or go-hee-gan. In Irish it is Mac (or Mag) Eochagáin, from Eochaidh. The initial "G" of Geoghegan comes from the prefix Mag, a variant of Mac and the anglicised form Mageoghegan was formerly much used.
The sept of the MacGeoghegans is of the southern Uí Néill, and said to be descended from Niall of the Nine Hostages. Niall was alive from the mid 4th century into the early 5th century. His father was Eochaidh Muigh-Medon, of the Celtic line of Erimhon, one of the sons of Esbain who it is said took Ireland from the Tuatha de Danann.
Niall's mother was Carthann Cas Dubh, daughter of the king of Britain. Niall's first wife was Inné, mother of his son Fiachu mac Néill, from who the Geoghegans are said to be descended. He also had seven other sons with his second wife, Roighnech. Niall's ancestry is claimed by Irish legend to trace back to Miledh of Esbain, King of Spain, whose wife was the daughter of the Egyptian Pharaoh Nectonibus. This is not to say Spanish-speaking Spain, which did not exist at the time, but a Galician or Gaelic-speaking community on the Iberian penninsula. From there the line is sometimes traced to Niul (from whom the river Nile got its name) who was married to the daughter of Pharaoh Cingris (all known only in Irish legend).
As High King of Ireland, Niall reigned from the ancient Irish royal seat at Tara, in modern County Meath. During his reign he conquered all of Ireland. He took a royal hostage from each of the nine kingdoms he subjugated, hence his famous nickname. He gave each of his sons a territory to govern. Fiachu was given a large area in the midlands. His descendants were known as Cenel Fiachaigh, anglicised at Kenaleagh and their territory was known by that name until Elizabethan times when it became the "Barony of Moycashel", County Westmeath.
Niall is also famous for bringing St. Patrick to Ireland as a slave. It is said that Fiachu refused baptism from the saint himself at Carn, near Castletown-Geoghegan. The old name for this place was Carn Fhiachaigh, or Fiachu's burial mound.
On the other hand, it is claimed in the early 15th-century manuscript called Leabhar Breac that the Geoghegans are descended, not from Fiachu, son of Niall, but from a plebeian, Fiachu, son of Aedh. This claim so enraged the descendants of Fiachu, that they killed the author of the passage, even though he was under the protection of Suanach, the abbot of the monastery of Rahin.
Time of Cromwell
The MacGeoghegan Barony of Moycashel is located in south central County Westmeath bordering King's County of the Uí Falighe. The main town in the barony is the old 'post and market' town of Kilbeggan, noted for its fine whiskey, its booming stud business and the modern Kilbeggan Race Course. The Sept were of considerable importance up to the conquest of Cromwell when they suffered severely primarily through confiscation and banishment. Their leadership of the 'Irish of Meath' alliance had dire consequences. This alliance had kept 'The English of Meath' in check since the thirteenth century when they dispossessed the De Lacy alliance of its castellated marvels in Trim. The collapse was due in no small measure to an appalling lack of political acumen in dealing with the Royalist and Commonwealth forces and their Parliamentary leaders. The Geoghegans gave no quarter and in the military mores of the day, received none in return. The Down Survey enabled the Commonwealth to moved quickly to dispossess the leading family of land, wealth and sway. It further facilitated a harsh exile of what both the Commonwealth and the later restored Monarchy both considered tp be a very dangerous opponent indeed. Given the rich agricultural potential of the lush Westmeath paddocks, confiscations came quickly, at the commencement of the Survey rather than the end with the most productive holdings going to Gustavus Lambart, a son of Lord Kilcoursey, later Earl of Cavan.
Some fifteen MacGeoghegan chiefs of Cenel Fiachaigh (Kinaleagh) are mentioned in the Annals of the Four Masters between 1291 and 1450. In the coming Tudor reconquest the (Nine Years' War) Richard MacGeoghegan, after fighting with great gallantry, was killed at the Siege of Dunboy in 1602. Five of the sons of Charles MacGeoghegan of Syonan, Co. Westmeath, were killed during the Williamite War in Ireland; and in the eighteenth century Mac Geoghegans appear as soldiers on the continent, mostly in the service of France. The extensive MacGeoghegan estates in Co. Westmeath were held by a number of different branches of the family. The most important of these properties was at Castletown-Geoghegan, followed by Jamestown, Rosemount, Carn and Donore. By the end of the seventeenth century the bulk of these vast estates had been confiscated and many of their original owners, who ranked among the leading gentry of the county, had been outlawed. Following the Stuart Restoration, the royalist were careful to keep many of the ex-parliamentary officials and ex Commonwealth soldiery on much former Geoghegan land. This precaution ensured physical and political loyalty. They also restored significant portions of post Down Survey distributions to former Geoghegan allies and Puritan opponents such as the Foxes, Molloys, Brennans, Coffeys and the Daltons. In return these families accepted grant and surrender oaths and religious civic commitments. Most of the Geoghegan leaders stubbornly refused to accept sign.
There have been several notable Geoghegans including:
- Michael Geoghegan (b. 1953), former HSBC Group chief executive
- Thomas Geoghegan (b. 1949), Chicago labour lawyer and politician
- John Geoghegan (b. 1956), Midfielder, Accrington Stanley FC
- John Michael Geoghegan (1881-1847) Fellow of the Royal Society of Edinburgh
- Helen Gahagan Douglas (1900–1980), American actress and Congresswoman from California whose electoral defeat to Richard M. Nixon propelled him into national politics.
- In the late 1800s William Geoghegan was head brewer, and his brother Samuel was chief engineer, at the Guinness brewery in Dublin.
- Ted Geoghegan (b. 1979) Director of We Are Still Here
- Roche MacGeoghegan (1580–1644), the Dominican, "saintly and enterprising" Bishop of Kildare;
- Richard Henry Geoghegan, linguist who designed the Esperanto flag.
- Richard MacGeoghegan who commanded the defenders at the siege of Dunboy at Berehaven Co Cork in 1601
- Conal MacGeoghegan, Chief of the Sept, translator of the "Annals of Clonmacnoise" into English in 1627
- Priest and historian James MacGeoghegan (1702–1764)
- Anthony Geoghegan (1810–1889), poet
- St. Hugh of Rahue between Tullamore and Tyrrellspass in Co. Westmeath) was of the family which became MacGeoghegan when surnames were adopted. The saint's crozier was in the possession of the MacGeoghegan family for many centuries. Through intermarriage, it passed to the Nagles of Jamestown House, Co, Westmeath.
- A branch of the MacGeoghegan sept settled in Bunowen, Co. Galway, and the name is found in that county as well as in their original territory. In the West it has been often shortened to Geoghan and even Gegan. In 1807, John Geoghegan of Bunowen Castle, Co. Galway assumed by royal licence the surname of O'Neill in lieu of Geoghegan and so his descendants.
- Lawrence and Sebastian Gahagan, who were sculptors of note in London between 1760 and 1820 were Irishmen called Geoghegan at home.
- John Geoghegan. Mayor of City of Woodstock, Ontario, Canada 1994–2003
- Simon Geoghegan Ireland rugby international.
- Máire Geoghegan-Quinn (b. 5 September 1950), Irish politician and current European Commissioner for Research, Innovation and Science.