Ó Coileáin is a Modern Irish surname generally belonging to the descendants of the last leading family of the Uí Chonaill Gabra, a sept and small but notable overkingdom of medieval and ancient Ireland, based in western County Limerick

County Limerick

It is thought that humans had established themselves in the Lough Gur area of the county as early as 3000 BC, while megalithic remains found at Duntryleague date back further to 3500 BC...

. Throughout much of their history the Uí Chonaill Gabra were in turn the leading sept of the greater regional overkingdom of the Uí Fidgenti

Uí Fidgenti

The Uí Fidgenti or Wood-Sprung People were an early kingdom of northern Munster, situated mostly in modern County Limerick, but extending into County Clare and County Tipperary, and possibly even County Kerry and County Cork, at maximum extents, which varied over time...

, considered among the highest ranked princes or flatha in all the Province of Munster

Munster

Munster is one of the Provinces of Ireland situated in the south of Ireland. In Ancient Ireland, it was one of the fifths ruled by a "king of over-kings" . Following the Norman invasion of Ireland, the ancient kingdoms were shired into a number of counties for administrative and judicial purposes...

. Ó Coileáin/Ua Cuiléin is most commonly anglicized O'Collins and O'Cullane. The surname has also long been found in County Cork

County Cork

County Cork is a county in Ireland. It is located in the South-West Region and is also part of the province of Munster. It is named after the city of Cork . Cork County Council is the local authority for the county...

, believed largely due to the migration there, probably in the late 12th or early 13th century, of a junior branch of the County Limerick dynasty.

Kings of Uí Chonaill Gabra

Carbery branch

It is believed that what is probably a junior branch of the Uí Chonaill kings joined their distant kin the O'Donovan family of the Uí Chairpre Áebda, another great sept of the Uí Fidgenti, in their exodus to Carbery in West Cork

West Cork

West Cork refers to a geographical area in south-west Ireland, lying within Ireland's largest county, County Cork. Traditionally a popular tourist destination, the area is seen as being distinct from the more populated northern or eastern parts of the county, as well as the more urban area of...

 between the late 12th and early 13th centuries.

Modern

• Michael Collins
  Michael Collins (Irish leader)
  Michael "Mick" Collins was an Irish revolutionary leader, Minister for Finance and Teachta Dála for Cork South in the First Dáil of 1919, Director of Intelligence for the IRA, and member of the Irish delegation during the Anglo-Irish Treaty negotiations. Subsequently, he was both Chairman of the...
  
  , believed his family were descendants of the Uí Chonaill Gabra. They belonged to the minor landed gentry of Carbery, and were situated in the right place, very near to O'Donovan country, for this to be quite plausible.
• Con Collins
  Con Collins
  Cornelius "Con" Collins was an Irish Sinn Féin politician.He was born in Arranagh, Newcastle West, County Limerick. He had joined the Gaelic League by 1910 when working in London for the civil service, as had Michael Collins the previous year. He was a member of the Irish Volunteers and of the...
  
  , County Limerick politician
• Mountcollins
  Mountcollins
  Mountcollins is a village in the extreme south west of County Limerick, Ireland, barely 100 metres from the border with County Kerry and just a mile from County Cork. The River Feale runs parallel to the village and is fed by the Caher River that divides the village.Mountcollins is in the Parish...
  
  , village in the extreme southwest of County Limerick