McCarthy Surname Study
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M(a)cCarthy (Irish Mac Cárthaigh) is one of the most common surnames in Ireland today and is particularly prevalent throughout Counties Cork and Kerry.  Through migration over the past four hundred years or more, McCarthys now reside in many countries throughout the world.

The McCarthy Surname Study was started in 2002 and seeks through Y-DNA analysis to identify the Y-chromosome genetic profiles of those with a paternal McCarthy (or variant thereof) ancestry, and in so doing to facilitate worldwide family connections among McCarthys.

It became very clear from the earliest results that not all male McCarthys could possibly claim ancestry in the eponymous Cárthach (d.1045), as suggested in historical writings, and the majority of us have probably acquired the name simply by being among the peoples over whom he or his immediate successors as kings of Cashel and Desmond held sway (clan affiliation) or by other means as suggested in Diversity in McCarthys below.

Both historically and in recent times McCarthys have been distinguished from one another by the branches of the McCarthy 'tribe' to which they belong, whether the leading families of the various MacCarthy septs (Mór, Reagh, of Muskerry, of Duhallow, Glas etc.) identifiable in the ancient histories as in use from ca. 14th century, or more recent agnomina which many present-day McCarthys are proud to cite, e.g. Cnoic / Cunic , Cremin / Crimeen, Cruig, Daunt, Farshing (Fairsinn), Guidagh (Gaibhdeach), Meenig (Muineagh), Norsa, Rabagh, Sowney.  In early 19th century Irish records these names often stand alone in place of 'McCarthy'; elsewhere they qualify it.  In some cases the sept names or agnomina have survived in their own right to eliminate the use of the McCarthy name altogether: McAuliffe, for example, was said to be a 12
th century branch of the royal family (although this has not so far been born out by Y-DNA testing). All such names are admissible to the Study where a McCarthy origin is conceivable. The Study seeks also to identify the Y-DNA profiles defining these branches and establish what, if any, are the relationships between them.

To understand the first millennium origins of the various McCarthy lineages, McCarthy Y-DNA data has been compared with that for other surnames where a similar genetic profile is observed. A series of phylogenetic trees - from around 2400 B.C. to the present day - depicting McCarthy members’ paternal lineage relationships among themselves and to those with other surnames is provided at This McCarthy Scrapbook site is used for files too large to be presented on these FTDNA web pages and also accommodates presentation material, a pedigree 'library', a bibliography, scholarly articles and a listing of McCarthy agnomina.


This webpage contains the following further articles:

  • McCarthys in Antiquity

  • Y-DNA Phylogenetic trees

  • References for McCarthy Genealogists

  • MacCarthy Courtesy title claims


Original - 10 May 2010.
Last updated – 30 May 2021.

1        Introduction

The following is written by an amateur genealogist and historian with a view to providing useful information for members of the McCarthy Surname Study, some of whom may be more knowledgeable, some beginners. The author will be happy to review, and correct where justified, any perceived errors. A modicum of understanding of DNA diversity is assumed: please refer elsewhere on the FTDNA website or to the most helpful ISOGG (International Society of Genetic Genealogy) website for the science of SNPs (Single Nucleotide Polymorphisms), the phylogenetic tree, STRs (Short Tandem Repeats), DYS (DNA y-chromosome Segment) values / alleles, the distinction between a haplogroup (of which subclade is used to indicate further subdivisions) and haplotype, and their use in genetic genealogy.

2        Brief history

The earliest evidence of homo sapiens in Ireland is from ca. 8,000 B.C., when it is believed he entered present day Co. Antrim from south-west Scotland, either by boat or via the landbridge still remaining as the last ice age closed and the sea levels were still rising.  Throughout the Irish Mesolithic and Neolithic periods (ca. 8,000 - 4,000 and 4,000 - 2,000 B.C. respectively) the inhabitants of Ireland came, as those of Britain, from among the descendants of those who had retreated towards the Iberian and Italic peninsulas during the last Ice Age and the peoples who already occupied these warmer climes, along with any new waves of migration from south-east Europe. In fact, recent examination of ancient bones in Ireland has revealed that the males of this period were almost entirely of Y-DNA haplogroup I2a1, although drilling down further and analysis of the rest of their genomes suggest the hunter-gatherers of the Mesolithic period became isolated and the influxes during the Neolithic period which largely but not entirely replaced them, brought new I2a1 subclades to Ireland. With the latter came a settled, farming way of life, along with megalithic tomb building, although these tombs are rare in the extreme south of Ireland, suggesting that the south of Munster was more thinly populated than the north in the Neolithic Age.

In the meantime, horse-riding, metal-working, males carrying Y-DNA haplogroup R1b (in the form of SNP R-M269) had begun, about 5,000 years ago (3,000 B.C.), to migrate westwards from Anatolia and the Caucasus, initiating the Bronze Age as R1b then swept through Europe, reaching Atlantic shores within the next millenium. It is believed R-M269 had occurred over 6,000 years ago on the Pontic Steppe of the Eurasian border, the Scythia of ancient history. SNPs R-U106 and R-P312, head two dominant haplogroups under R-M269. It is estimated these occurred about 4,700 years ago (or ybp, years before present). The vast majority of Irish men today belong in the haplogroup of SNP R-P312, and in particular its own subclade marked by SNP R-L21, estimated to have occurred about 4,400 ybp, and then the 'son' of L21, R-DF13, which occurred very soon after. Similar high percentages of L21 and DF13 are also seen in Wales, while their haplogroups are also dominant throughout Scotland, the west and north of England, and Brittany. Alternative theories place the occurrence of SNP R-L21 itself in the Rhineland / Eastern France region, on the continuing march of P312-carriers westwards, or on the North Atlantic seaboard, whence it radiated back eastwards.

The discovery of rich copper deposits in south-west Munster increased the influx of migrants and traders into this region during the Irish Bronze Age (ca. 2,000 - 500 B.C.), the trickle of newcomers from Britain and Continental Europe continuing through the Iron Age, the Viking invasions, and up to and beyond the 12th century A.D. 'Anglo-Norman' invasion, each new arrival being assimilated into Munster culture and society. We await with interest the Y-DNA analysis of any ancient bones from south-west Munster from the Bronze and subsequent Iron Age periods.  

The most difficult aspect of Irish genealogy for many is the lack of parish records much before 1815 in rural areas and the later 1700s in the major towns. However, although following a paper trail back through the 18th century may be impossible for many, what lies beyond is a unique store of genealogical information stretching back many centuries. It is claimed that it was the custom of the peoples who occupied Ireland 2,000 or so years ago to designate a member of each community (or “tribe” or “family”) who would learn, remember and recite its genealogies. In the middle of the first millennium, these began to be written down. In due course the earliest scripts were lost, but successive copies retained the information, albeit flavoured with mythology, distorted by inventiveness or corrupted by political correctness. Christianity came to Ireland in the 5th century, and when monks began to participate in the role of the scribe, the genealogies became woven with biblical connections, placing them in a context which tied together all strands of known history. But whether fact or fiction, we do have a lineage claimed to have produced the leading MacCarthy families and which goes back before these earliest written genealogies. Written sources from about the 11th century onwards indicate that this MacCarthy family derived from the Eóghanachta of southern Ireland, who are claimed to have also spawned the McAuliffes (from Tadhg MacCarthy), McGillycuddys, O’Callaghans, O’Donoghues, O’Keefes, O’Mahonys, O’Sullivans, O'Moriartys and others. The Eóghanachta took their name from the third century A.D. Eóghan Mór (Eugene / Owen the Great), son of Ailill Ólom (aka Olioll Olum), King of Munster. However it is suggested that the identity 'Eóghanacht' only came into being following the era of Eoghan Mór’s gt gt grandson (Conall) Corc, in the 5th century A.D. On the death of King Ailill Ólom, his kingdom was allegedly divided into Desmond (south Munster), ruled by Eoghan Mór (or a son thereof), and Thomond (north Munster), by Eoghan’s brother, Cormac Cas (from which the term dál gCais, or Dalcassian, is derived to describe its peoples). Most historians now consider this story to have been fabricated at some stage to provide the image of a unified population. Certainly the genetic signatures of those who it is suggested have 'Eóghanacht' and 'Dalcassian' Y-DNA haplotypes are not consistent with common ancestry as little as 1,600 years ago. Even though there is remarkably good alignment of the (phylo)genetic tree with the progeny of Eoghan Mór according to the literature for a number of surnames and though 20% of present-day McCarthys have origins sprinkled throughout this tree, this is not the provenance of the eponymous Cárthach, king of the Eóghanacht of Cashel, who was killed by the Lonergan clan in 1045. We have shown through Y-DNA testing that his progeny, who account for 30% of present-day McCarthy males, is of an altogether different provenance.

Pedigrees have been published displaying the many branches of the family deriving from Cárthach's grandsons Tadhg (or Teig) and Cormac – there was possibly also a brother Donncha(dh) (or Donogh)  - dividing in subsequent centuries into a number of “septs”. Cárthach's son, Muireadhach mac Cárthaigh (son of Cárthach), was the first to adopt the surname of McCarthy (as it is most commonly anglicised today).  Fig.2 at provides a tree for many of his progeny based largely on information from annals and ancient genealogies. It  indicates derivation of the most prominent septs -  the senior line of MacCarthy Mór, which eventually migrated to Co. Kerry, MacCarthy Reagh (Riabhach) based in Carbery, in south-west Cork, the MacCarthys of Duhallow in north-west Cork, the MacCarthys of Muskerry, and the Sliochd Feidhlimidh of Gleannacroim (in the vicinity of Dunmanway) - plus a number of further secondary septs. (Note this now includes indication of a approximate positions of SNPs where the findings of Y-DNA investigation are considered to align with the historical tree. This is explained on the Results page on this website).

3        Diversity among McCarthys

As indicated in Fig. 1 on our Scrapbook website, SNP testing and predictions reveal that about 10% of  McCarthys belong to haplogroups E1b1b1 (E-M35.1), G, I1, I2a1 and R1a1, with the remaining 90% falling in the haplogroup of SNP R-M269. As with R-M269, the I1 and I2a1 clades prevail not only in Ireland, but also in Western Europe, I1 being prominent in Scandinavia, and I2a in several locations in Southern Europe. E1b1b1 is believed to have appeared in N. W. Greece about 8,500 years ago and its subclades have strong Mediterranean / Adriatic connections (ref 1). Each of these other haplogroups had gone their separate ways before the last ice age, so clearly their members do not share mediaeval, Iron Age or even Bronze Age paternal ancestry with the R-M269 McCarthys.

Between 81 and 87% of all McCarthys share common paternal ancestry in the aforementioned R-L21 progenitor (along with 70% or more of other Irish men). However, significant differences in their haplotypes are proof of divergence soon after, and thus that these R-L21 McCarthys too comprised a number of different lineages each with their own origins – common ancestors - emanating from the Bronze Age, long before the birth of Eoghan Mór or Cárthach.

The Trinity College, Dublin, Irish DNA project of around 2003/04 by D G Bradley and B McEvoy identified through STR testing that many O’Neills and carriers of other surnames common in north-west Ireland appear to descend from two particular common ancestors, and that calculations of the time to the more distant of these was consistent with him being the legendary Niall of the Nine Hostages (ca. 400 A.D., but note that the benefit of more extensive testing has subsequently shown his time to be much earlier than Niall). But others of these same modern-day surnames clearly did not share these ancestries. A similar situation exists for the name McCarthy and its variants. A McCarthy surname pertaining to a bloodline other than that of Cárthach, King of the Eóghanachta of Cashel, could arise from, for example:

•Soldiers, serfs, or slaves or hostages taken in battle and who remained with their captives, all under the tutelage of a McCarthy king, chief or chieftain, adopting this surname.

•Rape of McCarthy womenfolk by invading forces.

•Other illegitimacy *

•Adoption (e.g. by a chieftain of a sister’s orphaned children) or taking a foster-father's name*.

•Raiders such as Vikings being absorbed, a century or two after they settled in Ireland,  into the group which became the McCarthy family as they became gaelicised.

•Stepsons taking the McCarthy name of their new stepfather (early deaths of husbands or wives, and thus remarriages, were common) *.

•Sons taking a mother's McCarthy maiden name for reason of its prowess. 

•The male progeny of Cárthachs other than he who died in 1045. Cárthach was not an uncommon name in 1st millenium Ireland and several Ui Cárthaigh (O'Carty) septs arose scattered about Ireland. In due course some of the (O')Cartys arising therefrom may have adopted the better known McCarthy name.

Some of the above are referred to as NPEs (Non-Paternal Events) in genetic genealogy. Items marked * could, conversely, similarly account for male descendants of the eponymous Cárthach bearing other surnames in the present day. See also the next paragraph for a further source of other surnames.

4            McCarthys in disguise

Whereas many have gained the McCarthy surname by the means indicated above, others have lost it through the use of agnomina to distinguish one McCarthy family from another and which subsquently supplanted the McCarthy name altogether. These agnomina could typically indicate a physical characteristic or disability in the founder, a location in which the family lived or a mother’s maiden name, and some could clearly lend themselves to other original surnames in different locations. And since the written form of names would vary according to the whim of the writer, interpreting the spoken word, further variations occurred as families migrated to parts of the world initially unfamiliar with Irish names. Thus a West Cork McCarthy family - known to the writer - which took Cremane as an agnomen in due course became the Creamer family following migration to London, with no hint any longer of its McCarthy origins. Similarly some nineteenth century baptism and marriage records refer, for example, to the surnames Farshing, Crimeen and Meenig, but it is often clear from research that these are McCarthys.


1.        Eupedia website (



1.  SNPs are denoted with a letter identifying the laboratory or accredited research group which discovered them plus the discoverer’s allocated reference number. Where two (or more) laboratories have made the same discovery, both numbers are quoted, in alphabetical order.


Original (as Subclades of R-L21) - 23 March 2012
Last updated - 31 May 2021

The International Society of Genetic Genealogy (ISOGG), a volunteer organisation respected by most parties involved in genetic genealogy, maintains a complete Y-DNA SNP tree at  New SNPs are added subject to proposal information meeting standards of acceptance. However, with the sheer volume of shared SNPs now being identified in families coming down into the most recent centuries, it has not been practicable to continue to maintain such detail universally. For those within the R-P312 Groups (about 88% of McCarthys and which are inclusive of R-L21), Alex Williamson’s The Big Tree at has been the recommended reference (apart from our Study's own trees) for early assignment of such new SNPs. Alex's tree utilises 'VCF Folders' (and preferably also raw data BAM files) submitted by Big Y and other Next Generation Sequencing (NGS) testers to the 'Y-DNA Warehouse' via the submission form at Since 2019, FTDNA's own Haplotree, to be found on members' Home pages under the 'Haplotree and SNPs' tab, has usually been the most advanced tree showing analysis of its own customers' NGS (i.e. Big Y-700) testing. Its Block Tree view of this Haplotree is modeled on Alex's The Big Tree. (Prior to 2019 newly discovered SNPs frequently first appeared on websites maintained by volunteers such as Alex analysing NGS test data or by other professional organisations offering such services and maintaining their own trees and of course this is still the case where testing has been with other companies). Assignment of SNPs to the most recent 'blocks' of FTDNA's Haplotree is often provisional until all quality control has been completed. Where such blocks are shared by Big Y-700 testers with participants who have not upgraded from Big Y / Big Y-500 to Big Y-700, it may be found that invalid assumptions have been made about the sharing of SNPs. The McCarthy Surname Study's own trees, focused on the interests of its members and incorporating exhaustive analysis of all their new test data, may prove more accurate in this respect. This analysis examines, as far as is possible, all elements of the information provided by FTDNA or other testing companies (and in due course analyses provided by other parties are reviewed to ensure nothing has been missed). 

Trees created and maintained by the McCarthy Surname Study indicate the phylogenetic disposition of McCarthys in the haplogroups of  E1b1b1 (E-M35.1), I1, I2a1, R-U106 and R-P312. For the last of these there are a number of separate trees: those pertaining to its R-U152 subclade then a series of trees for subclades of R-L21. The Study's trees combine definition provided by SNP testing (where available) with postulation based on STR testing and are presented on the McCarthy Scrapbook pages at The trees for Irish Type II haplotypes (which include McCarthys in the Study's R-L21 Group A) and the R-Z16526 haplogroup (which incorporate those in the Study's R-L21 Group B as a subset of the overall R-Z16526 tree) are comprehensive. Trees for the remainder largely use Alex Williamson's work (where applicable) and FTDNA's haplotree as a guide to the phylogenetic structure within which the McCarthys fit then show detail only for those non-McCarthy test kits which are closely related.

For the approximately 50% of McCarthys whose paternal ancestry does not fall within McCarthy R-L21 Groups A and B there is usually much useful information, and sometimes phylogenetic trees, to be found on websites associated with their respective ancestral haplogroups.


Original - 30 March 2012
Last updated - 04 June 2021

1.  Tracing Your McCarthy Family Tree

Richard McCarthy, one of our Study's members, has collaborated with the undersigned in producing a two-book set Tracing Your McCarthy Family Tree, to be made available on Amazon. Book 1 (which is already available in a Kindle version) targets complete novices (although is full of tips and hints which more seasoned researchers may have missed) and concludes with the ordering of a Y-DNA test and joining the McCarthy Surname Study. Book 2, expected to be available by mid-June 2021, will explain the nuts and bolts of Y-DNA testing and the work of the McCarthy Surname Study. Both should very soon also be available in paperback versions.

Also of note for those with Co Cork origins, 'Skibb Girl' provides an excellent resource in which will be found numerous M(a)cCarthy references, at

2.  Genetic Genealogy is the home of the Munster Irish DNA Project. It is focusing on the pre-Anglo-Norman occupants of the province of Munster, and thus will be of interest to those fascinated by their possible first millennium A.D. ancestry. It invites participants with prescribed surnames (including, of course, McCarthy and variants) identified in ancient genealogical tracts as belonging to Munster and who either have successfully traced their origins to the province or whose haplotype belongs to one of a small number of specified groups specifically or strongly associated with Munster. At present these are restricted to Irish Type II (of R-L21 Group A of this McCarthy Study), the L362 subclade (R-L21 Group B) and Irish Type III (R-L21 Group F3).  However, it is possible that some other modal haplotypes which form specific branches of other haplogroups /subclades may be added as research continues. 

3.  Reading lists

A short list of useful reference books and manuscript transcriptions of relevance to McCarthy ancestry is provided on our on the McCarthy Scrapbook pages at Many of these are available free of charge online.

“Desmond” is an anglicisation of the Irish for South Munster and is generally the area in which the MacCarthys held sway for many centuries.  The Kingdom of Desmond Association website, at (see also next section), has much information on McCarthy history and provides a further excellent reference list of literature pertaining to McCarthy and Desmond history. However, as with all histories and genealogies relating to the origins of the MacCarthy kings of Cashel and Desmond, the authors did not have the benefit of Y-DNA test results. As discussed in more detail on the Results page on this McCarthy Surname Study website, this testing clearly shows that somewhere beyond Cárthach's great grandfather, Ceallachán of Cashel, the paternal ancestry of these kings derives from an entirely different bloodline than that indicated in the literature. These paternal ancestors may have lived among the Eóghanacht peoples for several centuries; they did not, though, descend in an all-male lineage from Ailill Ólom, Eoghan Mór, Ailill Flann Bec or Conall Corc. The provenance of 20% of McCarthys has nonetheless been shown to align with ancestry in Ailill Flann Bec and his ancestors; these acquired the surname by means other than descent from the progeny of the eponymous Cárthach. References to the paternal ancestry of the MacCarthy kings of Cashel and Desmond should be read with this caveat in mind. 


Original - 30 March 2012
Last updated - 04 June 2021

Closely associated with the Kingdom of Desmond Association website has been the MacCarthy Clan Foundation, at (currently offline). At the end of the 1990s, a Clan MacCarthy Society fell from grace when a then claimant to be entitled to call himself the MacCarthy Mór, along with a string of other titles, was accused of being fraudulent. This eventually led to the discontinuation of the whole practice of the granting of such “courtesy titles” by the Irish Genealogical Office. These two new sites are unconnected with the now defunct Clan MacCarthy Society and are attempting to restore and build on some of the valuable contributions the latter nonetheless made.

The MacCarthy Clan Foundation, with the support of The Kingdom of Desmond Association, has persevered in the 21st century with the concept of a modern day MacCarthy Mór, claiming he should come from among the members of the most senior MacCarthy line traceable, i.e. the closest descent by primogeniture to the last true MacCarthy Mór, Domhnall Mac Cárthaigh Mór (died 1596), if we ignore transfer of the title to his son-in-law Florence MacCarthy Reagh. While it is not the intention of this Study to pass judgement on the merits of such titles being revitalised in the 21st century, we are certainly able to comment on the validity of claims with respect to genetic evidence.

Samuel Trant McCarthy, author of the invaluable work The MacCarthys of Munster, published in 1922, had claimed the MacCarthy Mór title as his own on the basis of descent from the Sliochd Cormac of Dunguile - see the left hand side of Fig. 2 on our aforementioned Scrapbook website - in the apparent absence of other contestants. A distant Trant-McCarthy relative has repeated this claim in the 21st century and indeed had it acknowledged by the heraldic office with jurisdiction over the north of England and Northern Ireland. Yet another distant relative of this family has taken a Y-DNA test and the result is certainly not inconsistent with origins in the Sliochd Cormac of Dunguile as suggested by Samuel Trant McCarthy. It is apparent that there is or are other members of our Study who descend from one or more brothers of this Cormac of Dunguile (i.e. from other sons of Tadhg na Mainistreach), and with this, possibly from his elder brother Domhnall an Daimh, the direct ancestor of the last true MacCarthy Mór, or even from the base son of  the latter, who is given studious attention on the MacCarthy Lordships page of the Kingdom of Desmond Association website. We are not as yet, however, in a position to adjudicate their relative seniority. 

N. McCarthy