Cosgrove Surname Project

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Surname History

The following Cosgrove surname history is a compilation of information collected from a variety of references on Irish surnames.  This compilation is imperfect as some of the information found in some references conflict with information found in other references.  While imperfect, this surname history does help members understand where in Ireland the various Cosgrove clans lived around the time of the Norman invasions in the early 1170s, all of which may aid in their genealogical research efforts.   The surname history, like other parts of this website, will continue to be updated as new information is discovered and validated.  If you have information that should be included in this surname history, please send me an email with your input as well as a reference that you used (book, website, journal article, etc). 

The two main surname variants, Cosgrove and Cosgrave, are derived from the Gaelic word“corcrac,” which means “victorious.” They are both variants of the Irish name O’Coscraigh (which means descendant of Coscraigh).  Most genealogical and surname references suggest that the name Cosgrove was most prevalent in Northern Leinster, Connacht, and Ulster Provinces, while Cosgrave was preferred in Munster Province and the remainder of Leinster Province.  However, it is widely known that Cosgrove and Cosgrave (along with other spelling variants) were interchanged for one another quite frequently so keep this in mind when you conduct your own personal research.  

Cosgroves in Ulster

Ulster was the homeland of three Cosgrove septs during the pre-Norman period.  Two were located in County Monaghan. One of the families, the O’Coscraigh, were Chiefs of Feara Ruis (or Fir Rois) (whichmeans “men of Ros”).  Ruis comprised of the lands affiliated with the Carrickmacross district (near modern day Carrickmacross) in the southeastern section of the county.  It is important to note that GeoffreyKeating, the famed Irish historian of the 17th Century, referred to the Carrickmacross sept as O’Cosgras, Mac Cuskers, or Mac Oscars “before they changed their name to Cosgrave” (notice he used the Cosgrave variant as opposed to the Cosgrove surname).  The other County Monaghan Cosgrove sept was the Mac Coscraigh/Mac Cosraigh (commonly associated with the MacCusker surname) who were erenaghs (hereditary stewards) of the church lands of Clones in the northwestern part of the county.  The various references stressed that the MacCoscraigh sept was a distinctly different family from that of the Feara Ruis O’Coscraighs though they both existed at the same time in close proximity to one another.  A third sept, Mac Giolla Coscair (son of the lad of victory), were the erenaghs of Derreybrusk in County Fermanagh.  If you believe you are related to these septs, I would recommend that you focus your research in either County Monaghan, County Louth, County Tyrone, or County Fermanagh depending on your own genealogical research findings.

Cosgroves in Connacht

The Connacht Cosgroves were chiefs of a district on the eastern shore of Galway Bay.  They were of Ui Maine ancestry and descended from Maine Mor, the Chief of the Clan Colla in the early 4thCentury.  Maine Mor was the fourth in descent from Colla-da-chrioch, one of the ancestors of the Oirghialla.  The Oirghialla was once a great Ulster clan that descended from the three Collas.  They conquered the ancient Ultonians who ruled Ulster at the time, after which the Oirghialla seized most of the Ulster region for themselves. Early Irish history listed two prominent members of this family line who served as bishops:  Coningus O'Coscraigh (d. 997 A.D) who served as the Bishop of Clonmacnois and Benedictus O’Cascry (d. 1325) who served as the Bishop of Killaloe.  Several historical references also state that the Galway O’Coscrais were closely related to the O’Madden family line as they shared a common ancestral line from ancient times.  If you believe you are related to this particular Cosgrove line, I would recommend that you focus your research in County Galway initially.

Cosgroves in Leinster

In the province of Leinster, Cosgroves were Lords of Feara Cualann (or Uí Briúin Cuallan), ruling  over areas consistent with the County Wicklow baronies of Rathdown, Arklow, and Ballinacor North and the southernhalf of Rathdown barony in County Dublin. This Cosgrove line’s hereditary Chief, or Clan Chief, was O’ Coscrach (Keating referred to him as O’Cosgraidh, O’Cosgry, or O’ Cosgrave”).  Their cinael, or kinship, was Dal NiadCuirp.  They ruled the lands that lie close to modern day Powerscourt in County Wicklow until they were disposed by the O’Tooles and O’Byrnes during the Anglo-Norman invasion around 1170.  Although Normans dispersed most of the sept, the Hearth Money Rolls and other 16th Century documents show landed gentry of the name in Counties Wicklow, Dublin, and Wexford.  This Cosgrove line’s progenitor was Brian,son of Enna Nia, son of Bressal Belach, son of Fiachu Baicced, son of CathirMor.  According to Keating’s History of Ireland, Cathir Mor had another son who started the O’Connor family of the Falghi line which also produced the O’Dunn, O’Dempsey, and Mac Colgan lines.  Another of Cathir Mor’s son was the originator of the O’ Gorman  line.  Other descendants of Bresal Belach and Cathir Mor were the O’Murphys, O’ Dowling, O’Ryans of Owney in County Tipperary, and the O’Kavanaghs.  Cathir Mor’s second greatg randfather was Cu-Corb of which produced the O’Dwyer line of Kilnamanagh.  William T. Cosgrave, the first Taoiseach ofthe Irish Free State and his son, Liam, Taoiseach of the Republic from 1973-1976 can trace their family line back to the Feara Cualann Cosgrove sept.  Another sept of the same name, often Anglicized as Cosker, is also found in Leinster near Bray in County Wicklow.  O’Coscrach also appears to be a sept from the clan Cinel Uchae that controlled parts of northern CountyKildare (Baronies of Ikeathy and Oughterany), part of County Offaly(Warrenstown), and part of County Meath (Upper Moyfenrath).  Keating pointed out that another O’Cosgraidh served as chief of Beantraidhe over what is now the barony of Bantry in Countyof Wexford.  Keating mentions that theMac Coscry’s or Cosgraves, an ancient clan in Wicklow and Queens county,changed their name to Lestrange but does not reference a date or the circumstances of when that occurs, though one can assume it was the result ofthe Norman invasion of Ireland during the late 1100s.   If you believe you may be related to any of these septs, I would recommend that you focus your research in the counties listed above. 

Cosgroves in Munster

Another Cosgrove sept named O’Cosgrans lived in Munster Province.  The O’Cosgrans were once Chiefs of Fera Maigne Feni, now Fermoy barony in Northeast County Cork.  They were eventually driven from their lands by the Anglo-Norman Roches.  According to Keating’s History of Ireland, the O’Cosgrans and the O’Duggans of Fera Maigne Feni, and the O’Cahils of Kerry originated from the same ancestral line as the  O’Connors of Kerry.  Keating noted that this territory consisted of seven septs that descended from Laeighsech Kenn-mor of the line of Ir.

Keating listed a Cosgarach in the lineage of O’Boyle of Boylagh in his History of IrelandIt is not known if this Cosgarach is connected to the Cosgrove surname.  Naill of the Nine Hostages was the second great grandfather of this particular Cosgarach. 

The Irish Times website contains a list of locations by county of Cosgrove (and other variants) family households in Ireland during the mid-1800s. The list also includes some name variants such as Cosgrave and Cosgriff.  The link to the website is


Keating, Geoffrey.  The History of Ireland, Vol III.  Kansas City, MO: Irish Genealogical Foundation, 1983.

Library Ireland. (2015). O'Coscraigh. Retrieved from Library Ireland:

Name Origin Research. (2015, March 21). Last Name: Cosgrove. Retrieved from The Internet Surname Database:

O' Hart, J. (2015). Irish Pedigrees; or the Origin and Stem of the Irish Nation. Retrieved from

Scubbly Images. (2016, March 21). Cosgrove Coat of Arms. Retrieved from

The Irish Times. (2016, March 21). Cosgrove Surname Search. Retrieved from The Irish Times Irish Ancestors: