# List of Irish clans in Ulster
## Northern Uí Néill

Niall of the Nine Hostages had seven sons, two of which, Owen (Eoghan) and Conall Gulban (Conaill) traveled north from the over-kingdom of Connacht and into the northern and western regions of the over-kingdom of Ulster, an area equivalent to modern-day County Donegal.
These two became the progenitors of the two Cenél's (or kindreds) that would make up the Northern Uí Néill; the Cenél Eóghain based in Inishowen, with their capital at Ailech; and the Cenél Conaill centered in the rich area of Magh Ithe, in the valley of the river Finn. For a time the Cenél Eóghain and Cenél Conaill alternated as kings of the Northern Uí Néill until the 8th century. The Northern Uí Néill would also alternate the High-Kingship of Ireland with their southern cousins the Southern Uí Néill into the 10th century.

### Cenél Conaill
## Cianachta

The Cianachta, or the race of Kane, also known as Clann Cian, descend from Cian, son of Oilioll Ólum, king of Munster in the 3rd century. The territory of the Cianachta spanned the present-day barony of Keenaght, which derives its name from them. By the 12th century, the Cianachta would be conquered by the Ó Cathaín.

### Cianachta Glenn Geimin

The Cianachta Glenn Geimin of Clann Cian, or the Cianachta of Glengiven, ruled a region now known as Dungiven.
| Sept (Common Forms) | | |
| Ó Conchobhair (O'Connor, Connor) | Meaning: Progenitor: | Territory: Glenn Geimin, present day parish of Dungiven Extra: Most powerful sept of the Cianachta, however were overthrown by the Ó Cathaín. Other forms of the name include: MacConnor, MacNaugher, MacNocker, MacNogher, MacNoher, and Nogher |

## Síl Colla Fochríth

The Síl Colla Fochríth, descend from Colla Fochríth, the first king of Airgíalla and one of Three Collas. Clans and septs that are claimed to descend from Colla Fochríth but with no other information given include; Ui Maine, Fir Dubhshlat, Ui Conaill, and Ui Luain.

### Imchad

Imchad was one of Colla Fochríth's sons, and from him son Muiredach Méth would descend the Uí Méith. The Uí Méith territory spanned northern County Louth, eastern County Armagh, and later in County Monaghan. John O'Donovan in his notes on the Annals of the Four Masters marks that there were two groups of the Ui Meith name; the Uí Méith Macha (or Uí Méith Tiri) and the Uí Méith Mara.
The Uí Méith Macha were based in the barony of Monaghan, County Monaghan. The Uí Méith Mara, meaning "Omeath by the sea", was seated in Cualigne in northern County Louth. The name Uí Méith survives as the present day name of the village Omeath.
| Sept (Common Forms) | | |
| Ó hAnrachtaigh (Hanratty, O'Hanratty, Henvey) | Meaning: Progenitor: Ionrachtach | Territory: Northern County Louth, and later County Monaghan Extra: Styled as lords of Uí Méith Macha by O'Donovan. Archaic forms include: O'Hanraghty. |
| Ó hAinbhith (Hanvey, O'Hanify, Hanfy) | Meaning: Progenitor: | Territory: County Monaghan Extra: Styled as lords of Uí Méith. |

### Cenél Rochada

The Cenél Rochada are descended from Rochad, one of Colla Fochríth's sons. The following terms are noted in the Annals to describe or group the clans and septs that would descend from Rochad:
* Uí Chremthainn – The Uí Chremthainn descend from Cremthann Liath, son of Fiac, son of Deig Duirn, son of Rochad. In effect the Uí Chremthainn consisted of multiple groups, part of the overall Airgíallan confederation. They ruled a territory spanning eastern Co. Fermanagh and northern Co. Monaghan.
* Síl Daim Argait – The Síl Daim Argait descend from Cairpre Daim Argait, son of Echach, son of Cremthann Liath, and are thus part of the Uí Chremthainn. Prominent groups include the Sil nDaimine and Clann Lugainn of the modern county Fermanagh area. Cairpre Daim Argait had three sons; Nadsluag, Lugain, and Daimine.
* Síl Duibthir – The Síl Duibthir are cited as being one of the "Trí Tuatha of Oirghialla" alongside the Uí Chremthainn and Fír Lemna. They descend from Duibthir, who in turn was descended from Cairpre Daim Argait, and are thus part of the Síl Daim Argait. The sept of Ua Laithéin are noted as chiefs of the Síl Duibthir.
* Uí Briúin Archaille – The Uí Briúin Archaille (also known as "Uí Briúin ar Chaill") descend from Brian son of Deig Duirn, who was a son of Rochad. This makes him the brother of Fiac from who the Uí Chremthainn descend. Their territory is described as being in the barony of Dungannon, Co. Tyrone.
* Dál nOaich – The Dál nOaich are cited as being descended from Cremthann Liath, who is also recorded as Cremthann Oach.
* Uí Labrada – The Uí Labrada descend from Labraid son of Deig Duirn, making him a brother to Brian and Fiac. Other than being noted in 1039 for slaying Murdoch mac Laverty O'Neill, the only other reference to them is the storming of their stronghold at Inis Uí Labrada by the Fir Manach.
* Uí Meic Brócc – The Uí Meic Brócc descend from Echdach Amainsen, son of Cremthann Liath. Not to be confused with the Uí Meics Brócc of the County Kerry Eóganacht.
* Síl nDaimine – The Sil nDaimine descend from Daimine, one of the sons of Cairpre Dam Argait, and are part of the Síl Daim Argait.

#### Clann Nadsluaig

The Clann Nadsluaig descend from Nadsluag, one of the sons of Cairpre Dam Argait, and part of the Síl Daim Argait. Their territory was in County Monaghan.
| Sept (Common Forms) | | |
| Ó Cearbhall (Carroll, O'Carroll) | Meaning: Progenitor: Cearbhall | Territory: Co. Monaghan Extra: Princes of Oriel until their power was destroyed by John de Courcy |
| Mac Mathúna (MacMahon, Mahon) | Meaning: Bear Progenitor: | Territory: Co. Monaghan Extra: Ruled Monaghan from the decline of the Ó Cearbhall from the early 13th century to the end of the 16th century. Related Septs: Mac Pilib (MacPHILLIPS) and Mac Ardghail (MacARDLE) |

#### Clann Lugain

The Clann Lugain descend from Cormac, one of the sons of Cairpre Dam Argait, and are part of the Síl Daim Argait. Their territory was in County Fermanagh.
| Sept (Common Forms) | | |
| Mag Uidhir (Maguire, McGuire, Guire, Guirey, Quirey) | Meaning: Dun-coloured Progenitor: | Territory: Co. Fermanagh Extra: Rose to prominence in around 1200, when Donn Mór Maguire established the sept in Lisnaskea, Fermanagh. Donn Carrach Maguire became the first Maguire King of Fermanagh in 1302, and between then and 1600, fifteen Maguires ruled as kings of Fermanagh. |
| Mac Gothraidh (Godfrey, MacCorry, Corry) | Meaning: Godfrey Progenitor: Gofraidh mac Donn Mór Maguire | Territory: Co. Fermanagh Extra: |
| Mac Maghnuis (MacManus, Mann, Manasses, Mayne) | Meaning: Manus Progenitor: Maghnus mac Donn Mór Maguire | Territory: Ballymacmanus island (modern Belleisle) Co. Fermanagh Extra: Second only to the Maguires in Fermanagh. Hereditary managers of the fisheries of the Maguires. Cathal Óg MacManus would compile the "Annals of Ulster" |
| Ó hÉighnigh (Heaney, Heeney, O'Heaney, O'Heeney) | Meaning: Progenitor: | Territory: Co. Fermanagh Extra: Amongst others ruled as kings of Fermanagh and Oriel until the rise of the Maguires. |
| Ó Maolruanaigh (Mulrooney, Rooney) | Meaning: Progenitor: | Territory: Co. Fermanagh Extra: Amongst others ruled as kings of Fermanagh before the Maguires. |
| Ó Dubhdara (O'Darragh, Darragh) | Meaning: Progenitor: | Territory: Co Fermanagh Extra: Amongst others ruled as kings of Fermanagh before the Maguires |

#### Clann Ceallaigh

Clann Ceallaigh descend from Cellach, son of Tuathal, king of the Uí Chremthainn, who in turn was descended from Daimine, one of the sons of Cairpre Dam Argait, and are part of the Síl Daim Argait. Clann Ceallaigh's name is preserved as the name of the modern barony of Clankelly in County Monaghan.
| Sept (Common Forms) | | |
| Mac Domhnaill (MacDonnell) | Meaning: Progenitor: | Territory: Counties Monaghan and Fermanagh Extra: Fermanaghs oldest recorded ruling family. Their power was broken by the Maguires and they migrated to the MacMahon country of County Fermanagh where they became sub-chiefs. |
| Mac Maolruanaigh (Macarooney, Rooney) | Meaning: Progenitor: | Territory: Clankelly, County Monaghan Extra: |
| Ó Flannagáin (Flanagan, O'Flanagan) | Meaning: Red, ruddy Progenitor: Flannacán mac Fogartach | Territory: Counties Fermanagh and Monaghan Extra: Their headquarters was possibly in the parish of Donaghmoyne. Noted as chiefs of Tuath Rátha (Toorah) in County Fermanagh. |
| Ó Baoighealláin (Boylan, Boyle) | Meaning: Progenitor: | Territory: County Monaghan Extra: Properly O'Boylan, this sept originally come from the same stock as the O'Flanagans in Co. Fermanagh and took over the kingship of the Dartraige (barony of Dartry) area of Monaghan in the late 10th century. By the end of the 11th century they controlled a vast tract of land from Fermanagh to Louth, and their chief was King of Fermanagh. By the 14th century however their power had been usurped by the MacMahon's. |

#### Fernmag

The Fernmag, or Fer Fernmaighe, is an area around Lough Ooney, aka Lock Uaithne near Smithborough in the barony of Dartry, Co. Monaghan. Immigration to south-eastern Monaghan brought the territorial name along with it, being preserved in the name of the barony of Farney. The genealogies given for the Fernmag claim they descend from Fergusa, the son of Nadsluaig, who was one of the sons of Cairpre Dam Argait.
| Sept (Common Forms) | | |
| Ó Lorcháin (Larkin) | Meaning: Rough or fierce Progenitor: | Territory: Barony of Farney Extra: Chiefs of Farney and the Uí Breasail of Co. Armagh |
| Ó Chríochain (O'Creehan) | Meaning: Progenitor: | Territory: Extra: Chiefs of Farney |

#### Fír Lemna

The Fír Lemna (also known as Uí Tuathail and Síl Tuathail) are cited as being one of the "Trí Tuatha of Oirghialla" alongside the Uí Chremthainn and Síl Dubthir. Its territory is thought to have been near Clogher, Co. Tyrone. The region of Magh Lemna is given as being in the parishes of Clogher and Errigal Keerogue in southern Co. Tyrone bordering Co. Monaghan. Their ancestry is cited as being from Tuathal, a son of Daimíne, making them part of the Síl nDaimini.
| Sept (Common Forms) | | |
| Ó Caomhain (O'Coen, Coen, Cohen, Cowan) | Meaning: Progenitor: | Territory: Extra: Cited as a king of Magh Lemna |

## Síl Fiachra Cassán

The Síl Fiachra Cassán, descend from Fiachra Cassán, a son of Colla Fochríth. Airthir (barony of Lower and Upper Orior), meaning 'east', was one of the main branches of the Síl Fiachra Cassán until the 8th century when it split into the main septs of the Uí Nialláin, the Uí Bressail, and the Uí Echdach. The territory of Airthir was centered in Ard Macha (Co. Armagh), along the eastern baronies of Orior. Some of the clans given as part of the Síl Fiachra Cassán include:
* Uí Cruind
* Uí Tréna – The Uí Tréna were located in Co. Armagh and claimed to be descended from Trian, son of Feidhlimidh (Phelim), son of Fiachra Cassán. Not to be confused with the Uí Tréna in Leinster or Munster.
* Uí Dorthain – Also recorded as the Uí Dorthinn, Dorthaind, Dorethainn, Tortain, they are cited as being possibly near Ardbraccan, Co. Meath. They descend from Dorthon, grandson of Feidhlimidh, son of Fiachra Cassán.
* Clann Sínaigh – This clan is described as being in Airthir (Orior) in County Armagh, with the genealogies showing descent from Fiachrac Cassán.

### Uí Echach

The Uí Echach, or the Uí Echach Airgíalla to distinguish them from the neighbouring Uí Echach Cobo of the Dál nAraidi, are suggested as ruling an area known as Tuath Echach, comprising the barony of Armagh in County Armagh. The Uí Echach Beg and Uí Echach Mór are noted as two branches of this group, but are also placed as being in Dál nAraidi and thus maybe part of the Uí Echach Cobo. According to the books of Lecan and Ballymote, the Síl Ciarain Uí Echach were located in Airthir.
The Uí Echach descend from Echach the grandson of Fiachra Cassán.
| Sept (Common Forms) | | |
| Ó Ruadhacain (Roghan) (O'Rogan, Rogan) | Meaning: Little red-haired one Progenitor: | Territory: Co. Armagh and barony of Iveagh Extra: Noted as chiefs of Uí Eochada, tributary to the O'Hanlons at the time, and as chiefs of Airthir. |
| Ó Domhnaill (O'Donnell, Donnell) | Meaning: World ruler Progenitor: Domhnall | Territory: Airthir Extra: Noted by O'Dugan as being a "noble tribe" of the Uí Echach |

### Uí Nialláin

The Uí Nialláin, or Clan Cernaich, descend from Nialláin, son of Féicc, son of Feidelmid, who was the son of Fiachra Cassán. Their territory lay in the baronies of Oneilland East and West in Co. Armagh, which both derive their name from the Uí Nialláin rather than the O'Neills. The Airthir kings of the Uí Nialláin sept ruled from Loch gCál (modern-day Loughgall).
| Sept (Common Forms) | | |
| Ó hAnluain (O'Hanlon, Hanlon) | Meaning: Outstanding champion Progenitor: Anluain mac Diarmada | Territory: Baronys of Oneilland East and West Extra: Lords of Orior and Oneilland, and with the MacGuinesses, controllers of east Ulster. Originally conciliatory to the English until the 17th century. They descend from Anluain mac Diarmada a descendant of Nialláin. |
| Ó hÉir (O'Hare, Hare) | Meaning: "Son of the angry one" Progenitor: | Territory: Extra: Ruled as a king of Airthir |

### Uí Bresail

The Uí Bresail, also known as the Uí Bresail Airthir, ruled an area in northern Co. Armagh along the southern shore of Lough Neagh (in the barony of Oneilland East) before they were displaced by the lords of Clanbrassil, the MacCann's.
| Sept (Common Forms) | | |
| Ó Gairbhith (Garvey) | Meaning: Progenitor: | Territory: Barony of Oneilland East Extra: Noted as being fierce chiefs, they held sway until being displaced by the MacCanns. |
| Ó Céileacháin (Callaghan) | Meaning: Companion Progenitor: | Territory: Liscallaghan, Co. Tyrone and Oneilland East Extra: Noted as chiefs of Uí Bresail Airthir. Archaic forms include (O')Kelaghan, Kealaghan, and (O')Keelan, however is as common in surnames, lesser names become lost to a more common name of similar sound, i.e. Ó Ceallacháin, a Munster sept that was first Anglicised as Callaghan. |
| Ó Longáin (Long, Longan) | Meaning: Progenitor: | Territory: Co. Armagh Extra: Cited as being of the western Uí Bresail' by O'Dugan. |
| Ó Conchobhair (Connors) | Meaning: Progenitor: | Territory: Extra: Cited as being of the western Uí Bresail by O'Dugan. |
| Ó Duibheamhna (Devany, Devenny) | Meaning: Progenitor: | Territory: Extra: Cited as being of the western Uí Bresail by O'Dugan. |

## Other Clans/Septs

| Sept (Common Forms) | | |
| Ó Ceanneidigh (O'Kennedy, Kennedy) | Meaning: Ugly head Progenitor: | Territory: Tirkennedy, County Fermanagh Extra: Claimed to descend from Fergus Cennfhota, a son of Cremthann Liath, and are thus part of the Uí Chremthainn. They ruled an area known as Tír Cennfhada, which is preserved in the name of barony of Tirkennedy, County Fermanagh. |
| Ó Daimhín (O'Davin, Davin) | Meaning: Ox Progenitor: Daimhín mac Cairbre Dam Argait | Territory: County Fermanagh Extra: Leading County Fermanagh sept up until the 15th century when the O'Neills and Maguires broke them. Noted as lords of Tirkennedy. The town and parish of Clogher gets its name from them; Clochar Mac nDaimhín. |

### Fir Rois

The Fir Rois were located in the barony of Farney, County Monaghan, and in the barony of Ardee, County Louth, and in Meath. Crích Ross stands 4 miles northwest of the point where the three counties meet.
| Sept (Common Forms) | | |
| Ó Coscraigh (Cosgrove, Cosgrave) | Meaning: Progenitor: | Territory: Carrickmacross, County Monaghan Extra: Chiefs of the Fir Rois in Carrickmacross, Monaghan Likely extinct |

## Síl Colla Uais

The Síl Colla Uais descend from Colla Uais, one of the Three Collas. Years before the Three Collas founded Airgíalla, Colla Uais ruled as king of Ireland until he and his brothers and three hundred followers were exiled to Scotland. Colla Uais had several sons including Eachach and Ercc.

### Uí Meic Uais

The Uí Meic Uais descend from Ercc, a son of Colla Uais. The Uí Meic Uais are cited as having several branches;
* Uí Meic Uais Mide, in the barony of Moygoaish, county Westmeath. Septs include the Ó Comhraidhe (O'Curry, Currie)
* Uí Meic Uais Breg, in the barony of Upper Kells and Lower Navan, county Meath. Septs include Ó hAonghuis (O'Hennessy, Hennessy)
Yet the following are cited by Francis Byrne as being collectively known as the Uí Meic Uais, though groups of this name are also noted in the midland regions:
* Uí Maic Caírthinn, south of Lough Foyle
* Uí Fiachrach Arda Sratha, Ardstraw, County Tyrone
* Uí Tuírtri, west and east of the Sperrings

### Uí Tuírtri

The Uí Tuirtri descend from Fiachu Tort, a son of Colla Uais. Their territory was said to have included an area west of Lough Neagh as well as north-west of Lough Neagh. One of the principal chiefs of the Uí Tuírtri was the O'Lynns, who ruled from Lough Insholin, Desertmartin, County Londonderry – the name of which is preserved in the modern barony of Loughinsholin. The Uí Tuírtri territory would expand into the lands north of Lough Neagh as they were driven eastwards by the Northern Uí Néill about the 10th century. At one stage the O'Lynns ruled a territory stretching all the way to the sea deep in Ulaid territory.
Cú Muighe Ó Floinn is cited as being king of the territories of Uí Tuirtri, Fir Lí, Dál Riata, and Dál nAraidi. Muircertach mac Thomas Ó Floinn the heir aspirant was slain "treacherously" by Hugh, grandson of Aodh Buidhe Ó Néill (progenitor of the Clandeboye O'Neills), and when his father Thomas died the realm passed into the hands of the Clandeboye O'Neills.
| Sept (Common Forms) | | |
| Ó Loinn (O'Lynn, Lynn, Lind, Linn, Lynd, Lindsay) | Meaning: Progenitor: Fhloinn mac Muiredach | Territory: Barony of Loughinsholin, county Londonderry and later baronies of county Antrim Extra: Originally spelt in Irish as Ó Fhloinn, however, the 'f' is aspirated in Ulster Irish thus is silent. Despite being regarded as a senior branch of Clan Rury of Ulidia, the Book of Ballymote gives a genealogy giving them descent from Fiachu Tuirtri. |
| Ó Domhnallain (O'Donnelan, Donnelan) | Meaning: Progenitor: | Territory: Barony of Loughinsholin, County Londonderry Extra: Cited as being chiefs of Uí Tuírtri in the 11th century. |

### Fir Luirg

The Fir Luirg, or men of Lurg, are listed as being among the Síl Colla Uais. By the 14th century, they were subjugated by the Maguires. Fir Luirg survives in the present-day name of the barony of Lurg, County Fermanagh.
| Sept (Common Forms) | | |
| Ó Maoldúin (O'Muldoon, Muldoon) | Meaning: Progenitor: | Territory: Barony of Lurg, Co. Fermanagh Extra: Chiefs of Fir Luirg |
| Ó Conghaile (O'Connolly, Connolly) | Meaning: Progenitor: | Territory: Ballyconnolly, Co. Fermanagh Extra: |

## Other Airgíallan Septs

| Sept (Common Forms) | | |
| Mac Canann (MacCannon, MacConnon, Canning, MacConnell, MacCann) | Meaning: Progenitor: | Territory: Clones, Co. Monaghan, then south Monaghan-north Louth area Extra: |
| Ó Cearbhalláin (Carlin, O'Carolan, Carolan) | Meaning: Progenitor: | Territory: Co. Cavan, then migrated across the provincial border into Co. Meath Extra: |
| Ó Cairre (Carr, O'Carr, Carry, O'Carry) | Meaning: Progenitor: | Territory: Co. Armagh Extra: In early medieval times the chief of the Ó Cairre sept was recorded as being "steward of Cenél Aengusa and royal heir of Oilech" |
| Mac Cairre (Carr, Carry, MacCarry) | Meaning: Progenitor: | Territory: Co. Armagh Extra: |
| Ó Conuladh (O'Connolly, Connolly) | Meaning: Hound of Ulster Progenitor: Henry Mac Con Uladh Mac Mathúna (Henry Mac Cú Uladh MacMahon) | Territory: Co. Monaghan Extra: Allegedly a sept of the southern Uí Néill driven north to Monaghan by the Normans, though it has been suggested that the Monaghan Connolly's descend from Henry Mac Con Uladh Mac Mathúna, who died as "tanist of Oriel", thus making them MacConnollys. If this is correct then their name is properly Ó Conuladh rather than Ó Conghaile. |
| Mac Oscair (MacCusker) | Meaning: Champion Progenitor: | Territory: Co. Fermanagh Extra: Branch of the Maguires |

## Uí Briúin Bréifne

The Uí Briúin Bréifne, or O'Brien Breffny, are a branch of the Uí Briúin kin-group. The Uí Briúin descend from Brion, son of Eochaid Mugmedon and Mongfind, and was an elder half brother of Niall of the Nine Hostages. The traditional territory of the Uí Briúin Bréifne was known as the kingdom of Bréifne, which included the modern Irish counties of Leitrim and Cavan, along with parts of County Sligo. It is speculated that Breffny derives its name from a pre-Celtic substrate language spoken in Ireland meaning 'ring' or 'loop', therefore making Breifne one of the oldest placenames in Ireland, dating prior to 500 B.C.
The two principal families of Uí Briúin Bréifne were the O'Rourkes and O'Reillys, who after a great battle in 1256, split the kingdom into East Bréifne and West Bréifne. The kingdom of Bréifne region remained part of the kingdom of Connacht until the time of Queen Elizabeth I when it was shired into the modern counties of Cavan and Leitrim, with Leitrim remaining within Connacht and Cavan becoming part of Ulster.
| Sept (Common Forms) | | |
| Mac Brádaigh (Brady) | Meaning: Progenitor: | Territory: East of Cavan Town, county Cavan Extra: Properly MacBrady, this variant has been rarely resumed. They were a very powerful Breffny sept controlling a large territory. The Cavan Crozier, staff of the early MacBrady bishops, is one of the few Irish croziers to have survived the Reformation. |

## Other Septs

Below is a list of other Irish septs in Ulster that can't be attached to any specific Cenél or Clann.
| Sept (Common Forms) | | |
| Ó Duibh Dhíorma (O'Duvdirma, O'Dierma, Dermond, MacDermott) | Meaning: Son of Black ? Progenitor: | Territory: Parishes of Upper and Lower Moville, Donegal Extra: Ruled a territory known as "an Breadach" |
| Mac Duibhinse (Mac D(h)uibhinse, Mcavinch(e)y, Mc Avinch(e)y, Macavinchey, adopted Vincent. | Meaning: Son of Black-man of the Island Progenitor: | Territory: Ulster, Counties Armagh, Londonderry, Monaghan, Tyrone, Dublin (1600s) and Limerick (1600s) Extra: A Sept / Family branch, who had their territory in counties Armagh, Londonderry and Tyrone in the Ulster province. Extra: The older record is Mcavinchey, Annie |
| Ó Glacain (Glacken) | Meaning: Progenitor: | Territory: Donegal Extra: |
| Ó Cadáin (O'Cadden, Cadden, Adam, Adams) | Meaning: Progenitor: | Territory: Roslea-Clones area, Fermanagh-Monaghan Extra: |
| Mac Cadáin (MacAdam, MacCadden, MacCudden, Adams) | Meaning: Progenitor: | Territory: Co. Armagh Extra: |
| Mac Ádhaimh (MacAdam, MacCaw, Adams) | Meaning: Son of Adam Progenitor: | Territory: Co. Cavan Extra: |
| Mac Gille Andrais (Gillanders) | Meaning: servant of (St.) Andrew Progenitor: | Territory: Co. Monaghan Extra: A distinct Irish name of the same origin as its Scottish counterpart |
| Ó Cnáimhsighe (Bonar, Bonner, Crampsey) | Meaning: Possibly mid-wife Progenitor: Cnáimhseach | Territory: County Donegal Extra: First recorded in 1095, it is one of Ireland's oldest surnames. As it derives from Cnáimhseach, which is a female name, Ó Cnáimhsighe appears to be one of the few matronymic Irish surnames. Archaic Anglicisations include O'Cnawsy and Kneafsey |
| Ó Buadhaigh (Boyce, Bogue) | Meaning: Victorious Progenitor: | Territory: Donegal Extra: Archaic Anglicised as Buie and Bwee, both of which were still used as synonums for Boyce in the early 20th century Donegal. |
| Mac Broin (MacBrin, Byrne, Burns) | Meaning: Raven Progenitor: Bran | Territory: County Down Extra: |
| Ó hUaruisce (Horish, Houriskey, Waters, Watters, Caldwell) | Meaning: Progenitor: | Territory: County Tyrone Extra: Ó hUaruisce is a variant of Ó Fuaruisce. The mistaken notion that the "uisce" in their name meant water led to many Anglicising their name to Waters. |
| Mac Conluain (Colavin, Cullivan, Caldwell) | Meaning: Progenitor: | Territory: County Cavan Extra: |
| Mac Giolla Chathair (Carr, Kilcarr, MacElhar, MacIlhair) | Meaning: Devotee of (St) Cathair Progenitor: | Territory: Co. Donegal Extra: |
| Mac Giolla Cheara (Carr, Kerr) | Meaning: Devotee of (St) Ceara Progenitor: | Territory: Co. Monaghan Extra: |
| Mac Cearbhall (Carroll, Mac'Carroll) | Meaning: Progenitor: Cearbhall | Territory: Co. Londonderry Extra: Distinct from the Ó Cearbhall sept |
| Ó Caiside (Cassidy, O'Cassidy) | Meaning: Progenitor: | Territory: Ballycassidy and erenaghs of Devenish, Co. Fermanagh Extra: Have been in Fermanagh for over a thousand years and until the Plantations were prominent in the fields of literature, medicine, and religion. They became hereditary physicians and ollavs to the Maguires, and later to many other clan chiefs across Ireland |
| Mac Laghmain (Clements, MacClement, MacClamon) | Meaning: Progenitor: | Territory: Co. Antrim and to a lesser extend counties Donegal and Londonderry Extra: |
| Ó Corcráin (Cochrane) | Meaning: Crimson Progenitor: | Territory: Co. Fermanagh Extra: Ecclesiastical family of Lough Erne |
| Mac Colla (Coll, MacColl) | Meaning: Progenitor: Colla | Territory: Co. Donegal Extra: Gallowglass family from Argyllshire introduced into Donegal in the sixteenth century. No connection to the Ulster MacCalls or MacCauls. |
| Mac Coileáin (Collins, Caulfield, Cullen) | Meaning: Whelp Progenitor: | Territory: Western Ulster Extra: |
| Mac Cuilinn (Cullen, MacCollin, Collins, MacCallen) | Meaning: Holly Progenitor: | Territory: Extra: |
| Ó Corra (Corr, Corry) | Meaning: Progenitor: | Territory: Counties Tyrone and Fermanagh Extra: |
| Mac Giolla Choscair (MacCusker, MacIlcosker) | Meaning: Progenitor: | Territory: Co. Armagh Extra: |
| Ó Coltair (Coulter) | Meaning: Progenitor: | Territory: Ballyculter, Co. Down Extra: |