The family name McILHAGGA
The surname McIlhagga appears in Surname Dictionaries published in both Ireland and Scotland, though interestingly all known to me refer to it as a Scottish surname. There is however a distinct difference in the way the etymology of the name is discussed on the two sides of the North Channel. This will be obvious if I quote George F. Black, 'The Surnames of Scotland' and Edward MacLysaght, 'The Surnames of Ireland'.
Black has “MACILHAGGA. Most probably for 'son of the gille of Mochuda'. See GILMAGU.” There follows five examples from 1527 to 1715, four in Ayrshire and one in Galloway. He then names three place-names in which the saint is commemorated in Scotland. His entry for GILMAGU has “Ir. Giolla Mo-Chuda, 'servant of (S.) Mochuda (=my Cuda), another name for S. Carthage of Lismore'”. He then quotes two Medieval charters referring to Abbeys in the Scottish Borders which are witnessed by Gilmagu in the 12th Century. He adds 'See also MACILHAGGA'. Black is followed by Diane D. McNicholl in 'The Surnames of East Lothian'.
MacLysaght has “Mac Ilhagga. Mac Giolla Chairge. This Gaelic form is given by MacGiolla Domhnaigh. A Scottish name found in Cos. Antrim and Derry. MacElhargy, MacIlhargy and Maharg are variants of it.” In MacLysacht's Supplement, 'More Irish Families', he has “MacIlhagga, Maharg. At first sight these two names would not appear to be variants, but when we remember that MacIlhagga is also found as MacIlharga, MacElhargy and McIlharg and that in Ulster Mac is frequently abbreviated to Ma the transition becomes intelligible. According to MacGiolla Domnaigh the Gaelic form is MacGiollaChairge which is common to Galloway in Scotland and to Cos. Antrim and Derry. Maharg is also written Meharg”. Further, Maclysacht has an entry under MacHarg, which says “Tyrone name is an earlier form of Maharg. See MacIlhagga”.
In Ireland it appears that MacLysacht has been followed uncritically, e.g. by Robert Bell in 'The Book of Ulster surnames' where he says 'Maharg is a variant of the Scottish MacIlhagga' (p.82), and by the Irish Times Internet site.
It also appears that MacLysaght has 'expanded' MacGiollaDomnaigh, where, in 'Some Anglicised Surnames in Ireland' (1923, p.45) there is no reference to MacIlhagga. He has “Meharg, Maharg – These two names are the shortened anglicised forms of McIlhargy. Other forms are McIlharg and McElhargy; in Gaelic the name is written MacGiolla-chairge, and is mostly found in Galloway and in Ulster, particularly in S.E. Derry”.
I have for the past twelve years done a 'One Name Study' (with the Guild of One Name Studies) of the name McIlhagga and its variants and have compiled Indexes of the name referring to thousands of births, marriages and deaths, and have come across no examples of the so-called variants quoted in MacLysacht, namely MacElhargy, MacIlhargy, Maharg, Meharg, McIlharg, McIlharga or MacHarg. The 'paper trail' appears to demonstrate that these names have a different origin to McIlhagga.
The result of the 'paper trail' appears to be confirmed by recent DNA analysis. A 'MacHargue / McHarg' DNA project has produced one set of results, up to 37 markers, and a McIlhagga DNA project has produced a totally different set of results, up to 37 markers. The McIlhagga results are part of group M269, sub-group R1b1a2* which is very rare.
I am no Gaelic scholar but my best thinking about the origins of the name McIlhagga is that if we go back to the 6th Century we may find our eponymous ancestor as a follower of (Saint) Mochuda Carthach. In Ireland it may be that followers have spawned a number of variants including McGillycuddy and McElhuddy. Parallel to such evolution we have what appears to be a migration to the South-West of Scotland, possibly a very early migration initiated by St. Colmon of Ella, where the name Gille Mochuda, via the Latin form Gilmagu evolved into McIlhago and McIlhagga. It was in Colmonell (named for St. Colmon Ella) in Ayrshire where the clan name appeared in 1527 in its Anglicised form, namely Macylhaggow.
Interestingly an internet site associated with an academic project at University College, London, which maps the whereabouts of Western Names, at www.publicprofiler.org/worldnames, confirms that the name McIlhagga is 'Group: Celtic; Subgroup: Scottish; Language: English'. For the variant McIlhagger it correctly changes the subgroup to 'Irish'.