History


The O'Reilly/Reilly Clan is one of the ancient families in Ireland that can be traced back in ancestry to the High Kings of ancient Ireland. The name has more derivations or variety in the spelling of the name than any of the other ancient family names and is one of the most numerous of Irish names.


Irish derivation: Ó’Raghallaigh
Name meaning: "Descendant of Raghallach" (extroverted one /sociable/ strong of arm)

OriginUí-Briuin Breiffne and the High Kings of Ireland

Coat of arms motto: "With fortitude and prudence"

Blood dripping from the Right hand: This symbolism is entirely unique to the O’Raghallaigh (O’Reilly) Clan. The symbolism to date is unexplained

The O’Raghallaigh Coat of Arms belongs to members of the O’Reilly Clan by genetic right rather than to any individual.
It represents an historic record of the O’Raghallaigh Clan and their status and achievements, fashioned in ancient Symbols and in harmony with the Clan’s history handed down from Ancient Times

Counties associated with the name: Found in every county in Ireland but principally Cavan, Longford, Meath, Westmeath, Fermanagh and Monaghan -also found in most countries worldwide.

Interesting Facts:  
Rulers of East Brefine:- 12th to 17th centuries
An increasingly popular first name in the US
Associated with the phrase The Life of Reilly

O'Reilly is the Anglicised form of the Gaelic Ó Raghallaigh and derived from a male ancestor's name, in this case Raghallach who lived in the 10th century. The name has more derivations or variety in the spelling of the name than any of the other ancient family names of Ireland and includes:

  • O’Raghallaigh
  • O’Raighilligh
  • O’Raghaill
  • O’Raoghallaigh
  • Rielly
  • Really
  • Realy
  • Reely
  • O’Reilly
  • Reilly
  • O’Reiley
  • O’Realley
  • Riley
  • Oreigle
  • Oragill
  • Oreille
The countries in which they settled after the Flight of the Earls transformed their name to accord with local pronunciations, for example, Orely in Spain, Oreille in FranceThe greatest concentration of the surname is found in County Cavan, formerly The Kingdom of East Breifne or Breiffne Uí Raghallaigh, one of the historic kingdoms of Ireland.

The Ancestry of the O'Reilly /Reilly clan and of others are recorded as deriving from Conn of the Hundred Battles (Conn Ced Chathach KI 123-157 AD), an early High King of Ireland, whose ancestors were High Kings of Ireland and from whom is sprung the Race of Conn that included most of the ancient families in the northern half of Ireland.

Many Irish Royal Families who ruled Kingdoms or Territories in Ireland during the Pre-Christian period were Chiefs or Lords of their Peoples in their Territory. One such cited Royal Family was that of Raghallach, the forebearer of the O'Reilly Clan that occupied the ancient Kingdom of Breiffne along with their blood cousins, the O’Rourkes (decendants of Ruarc). Aed Finn mac Fergna d.611 who was the fifth in descent from Dui Galach KC (King of Connaught) d.463 who was converted by St. Patrick, was a common ancestor of the O’Reillys/Reillys, the O’Rourkes, the McGoverns/McGaurans, McKiernans and MacBradys.

Dui Galach KC d.463 was a son of Brión KC (Brian) from whom all the Ui-Briuin sept are descended and the O'Rourkes and O'Reillys and their co-relatives were referred to as of the Ui-Briuin Breiffne with the name of their territory (Breiffne) added to distinguish them from  other Ui-Briuin septs or clans who were also descendants of this Brian (Brión KC) and who were seated in other parts of Connaught.
The Kingdom of Breiffne or Bréifne (anglicized Breffny, Brefnie or Brenny) included the modern Irish counties of Leitrim and Cavan, along with parts of County Sligo (an area roughly equivalent to the modern Roman Catholic Diocese of Kilmore). Breiffne is derived from an old Irish word meaning 'hilly', a description which describes the topography of this part of Ireland. In the early 12th century, when Tigernán Ua Ruairc was king of Bréiffne, the area extended from Kells in County Meath to Drumcliffe in County Sligo. First references to the O'Reilly's in official records shows them ruling an area to the north of Lough Ramor. The heads of this clan were Chieftains or Kings of the territory of East Breiffne from the 12th to the 17th centuries. 

The Chieftain was often called Breiffne O’Raghallaigh (Breiffne O'Reilly) or the O’Raghallaigh or Lord of the Kingdom of East Breiffne to distinguish him from the Lord of West Breiffne who was usually called Breiffne O'Rourke. The O’Rourke Clan was the more powerful clan initially and they gained dominance and ruled over Breiffne for generations. After a major battle between the O’Rourkes and the O’Reillys in the 12th century, the O’Rourkes were never again strong enough to dominate the O’Reillys and the O’Reilly Clan controlled and ruled over East Breiffne for almost the next five hundred years up to the Plantations of Ulster and the Cromwellian wars.

After the split, the fortunes of the O’Reilly Clan improved and that of the O’Rourke Clan declined. The O’Reillys governed the whole of County Cavan and part of Leitrim, thus reclaiming much of the territory given to the O’Rourkes. They also spread their influence into Counties Longford, Westmeath, Meath and Louth as far as the Pale and traded with the Pale and further afield.

The O’Reilly Chieftains were true to their ancestors in Celtic traditions and served as Kings and Princes of Breiffne. The ancestral inauguration site of the Kings and later Chieftains was at the ancient stone circle on Seántomon Hill (pronouncedShantomon) – a hill approximately 3 miles (5km) north-east of Cavan town off the road to Ballyhaise on the summit of which there are the remains of a Druid temple consisting of several huge stones standing upright and referred to as Fin MacCumhail’s (Fionn McCool's) fingers.

The Chieftain of the O’Reillys was known as Breiffne O’Rathallaigh or the O’Raghallaigh (the O’Reilly) in line with Celtic tradition and in the middle ages, his influence also extended well into Meath and Westmeath and surrounding areas. 

In later times they moved the inauguration site to the Hill of Tullymongan above the town of Cavan (the hollow) then called Baile O’Raghallaigh.In the 13th and 14th centuries the family became very powerful and was widely involved in trade in medieval Ireland. Their total domination of the area is reflected in the fact that they issued their own currency which was legal tender throughout Europe until the 15th century when banned by the English. At one time reilly was a term for Irish money and it was said that the O’Reillys lived well as the phrase The Life of Reilly indicates. On the other hand, it was said that someone who was financially challenged hadn’t a Reilly to his name. 

Giolla Iosa Rua O'Reilly, Chieftain of the O’Reilly Clan, founded a Dominican abbey at Cavan in the year 1300 and for three centuries this was a flourishing ecclesiastical area and burial site of the Kings and Princes of Breiffne as well as that of Owen Roe O’Neill in the 1640s. In 1393 the Dominicans were expelled by the O’Reillys and the Abbey was given to the Franciscans.

The name cabhán (meaning hollow) referred to the area or hollow below the O’Reilly castle on Tullymongan Hill.  In this hollow, around the Abbey,  the town now called Cavan developed.

On Tullymongan hill, on the site of the castle, a plaque reads:

"The O’Reilly Castle:
One of the most important buildings in the history of Cavan town, was built sometime in the fourteenth century at the peak of Tullymongan Hill, replacing the old O’Reilly stronghold at Clough Oughter.
Such a commanding view on the top of Tullymongan was important both for defence and security of the town, which began to grow in earnest from this time on.
Indeed, the position of the castle in such a prime site, observing Cavan town, reflects the importance and control of the O’Reilly family in the area.
A map from the late sixteenth century depicts the castle as a square building several stories high with a door in its west wall.
The castle was portrayed as several stories high with a castellated roof and two wings either side of a large semi circular doorway.
There was a staircase at the south and corner turrets at the north-west and south-east both of which rose above the roofline of the main building.
The castle was damaged a number of times throughout its history between the fifteenth to the seventeenth centuries. But it was still a major stronghold in 1690, when the castle was at the centre of a major battle, as part of the Williamite/Jacobite wars, during which Cavan town was almost completely destroyed.
Following this, the castle slowly fell into disrepair during the eighteenth century and its stone used for various building projects throughout the town until nothing was left of this once imposing structure."

Breiffne (meaning hilly) is a good description of the countryside particularly towards the northwest where the landscape is composed of drumlins and in between the rolling hills, the valleys were poorly drained with extensive bogs, swamps and lakes. This geography helped the O'Reilly Clan retain independent control in East Breiffne even after the Normans arrived in Ireland in 1169. The difficulty of traversing the Cavan terrain with its many thick forests, hidden valleys, watery bogs and lakes combined with the skill of the O'Reilly cavalry and the intractability of the O’Reilly clan and their supporters, kept the Norman invaders successfully at bay for several centuries. The O'Reillys maintained their independence from English rule until the rebellions of the early 1600s, the Plantation of Co. Cavan (East Breiffne) and finally the Cromwellian wars.


The Kingdom of Breiffne region was part of the kingdom of Connacht up until the time of Queen Elizabeth I. In 1584 it was shired into the modern counties of Cavan and Leitrim, The County of Leitrim remained a part of the Province of Connacht whereas the County of Cavan became part of the Province of Ulster. Later in 1608 the boundaries between the counties of Cavan and Leitrim underwent further changes in order to perfect the plantation of County Cavan where a portion of County Leitrim was incorporated into County Cavan to form the present regions of Cavan and Leitrim.