Geographic origins
The name Kennedy arose separately in Gaelic Ireland and Scotland, initially as a patronymic. More rarely it was adopted by Hungarian Jews (more commonly spelt Kenedi). Sometimes similar sounding but unrelated names have morphed into Kennedy, eg Kempty in Aberdeen. It also occurs, rarely in Scotland, as a given name but almost exclusively in the south west.
Early Irish Kennedys
The Irish Annals record one Cennetig son of Lorcan, whose son Brian would rise to fame as Brian Boru, claimed High King of all Ireland. Cennetig can be found in the Annals of Inisfallen eg AI951.3 'Mors Cennétig m. Lorcain, rígdamna Cassil' ('Death of Cennetig son of Lorcan, royal heir of Caisel'). In later decades there are many references to Brian who is usually described as 'Brian, son of Cennetig'. The Annals of Inisfallen survive in a manuscript copy dating to around 1095 and were compiled in Munster; they thus show a strong bias to the Munster kings. Other annals award Cennetig less glamorous titles. Furthermore historian Kathleen Hughes believes the death record of Cennetig was inserted retrospectively. There were other, earlier, Cennetigs, for example one Cennetig mac Gaethine of the Loiges (Leinster) fl. 862 AD and thus Cennetig son of Lorcan cannot literally be considered 'the first Kennedy'. O Brien's Corpus Genealogiarum Hiberniae, compiled from Rawlinson B.502 and the Book of Leinster lists 11 Cennetig individuals.
Early Scottish Kennedys
Updated 8.12.09
Scottish records simply do not exist from the time period that the surname was emerging over in Ireland making direct comparisons impossible. The Book of Deer with its Gaelic notes, dating from around 1120 AD, is an exception. Fortunately it contains both a Kenneth and a Kennedy literally side by side, clearly demonstrating that there is no etymological connection between the two names. Professor Kenneth Jackson, who held the Celtic chair at Edinburgh previously held by William Watson, identified Cormac mac Cennetig as synomymous with modern Kennedy. One possible Irish source for the Scottish branch is discussed here.
In the 13th and 14th centuries a number of individuals appear in Scottish records with the surname Kennedy or MacKennedy, but their pedigrees cannot be determined and their distribution is too spread out to draw useful conclusions. What is not in doubt is that the Kennedy family of Dunure in Ayrshire were made Chief of their name by royal charters by the mid-14th century, and hence the tendency to associate them with the birth of Kennedy as a hereditary surname in Scotland is reasonable, even though they were no more 'the first Kennedy' in Scotland than Cennetig mac Lorcan was in Ireland. The 1185 death record of a Henry Kenedy in a battle in Galloway is not contemporary but from the late 14th century account of Fordun, whose sources appear lost; he is not mentioned by name in the contemporary Melrose Chronicle.
The origins of the highland Scottish Kennedys are very unclear, clan legends notwithstanding. Certainly they were at Leanachan in Lochaber in the early 1600s and possibly earlier. They had started to congregate in northern Perthshire by the mid to late 1600s and feature in the Logierait area, one of their biggest concentrations, by the time of the 1691 hearth tax, as well as being present in the baptism register of that parish as soon as it opened in 1650. Before that, various singleton records going as far back as the early 15th century have been noted but are thought unlikely in themselves to have led to settled populations, especially where consisting of ecclesiastical appointments. Certainly the registers of Inverness burgh indicate that the Kennedys did not arrive that far north until almost 1700, despite a Duncan Kennedy witnessing a document there in 1548 and a John Kennedy being seised of lands further north still in Dornoch in 1579. The level of connection with the lowlands is unproven and more Kennedy DNA particularly from Lochaber and Rannoch is needed to fill the picture.
Etymology
Gaelic scholars have proposed several different ideas about the etymology of the name. Professor William Watson (a native speaker and Professor of Celtic Languages) gave it as 'grim-headed'. Professor Kuno Meyer, first Professor of Celtic Languages at the Royal Irish Academy, gave it as 'ugly-headed'. Whilst there is little argument about the first syllable deriving from 'ceann' for head, a subtle but important variation was introduced with the idea that the adjective following it was actually 'helmeted'. I have discussed this particular point in a separate article. Alternate ideas such as a derivation from Kenneth, or indicating 'head of the kindred', are not favoured by this project.
References
Cottonian MS. Faustina B. ix, British Museum ('Chronicle of Melrose Abbey')
Bodleian MS. Rawlinson B 503 Annals of Inisfallen accessed online at CELT
Corpus Genealogiarum Hiberniae, MA O'Brien (Dublin, 1962)
New history of Ireland Vol. 1 Prehistoric and early Ireland, ed. Daibhi O Croinin (Oxford, 2005)
Brian Boru Ireland's greatest king, Maire ni Mhaonaigh (Tempus, 2007)
Early Christian Ireland, Introduction to the sources, Kathleen Hughes (London, 1972)
Dictionary of the Irish language based mainly on Old and Middle Irish material, Royal Irish Academy 1913-76
Contributions to Irish lexicography, Vol. 1 A-C, Kuno Meyer (1906)
Etymology of 'Brian Borumha', Kuno Meyer, in Eriu iv, 68 (1910)
Gaelic notes in the Book of Deer, Kenneth Jackson (Cambridge, 1972)
Celtic place-names in Scotland, William Watson (Blackwood, 1926)
Calendar of entries in the Papal Registers relating to Great Britain and Ireland (1198-1471)
NAS GD25 Ailsa Muniments (1290-1940)
NAS GD44 Gordon family papers (1357-1903)
NAS GD176 Mackintosh of Mackintosh papers (1442-1930)