The Kennedy's (Cennetig) are in the family from the beginning

Cennetig (Kennedy) of the Dalcassians
The majority of the Kennedys who settled in Northern Ireland are of Scottish origin from the territories of Galloway and Ayr just across the Irish Sea some twenty miles away. These Scottish Kennedys intermarried with local Irish and thus they are Scots-Irish in blood. The other Kennedy family is located in southwest Ireland with its foundation in the bloodline of Cormac Cas, King of Thomond and Munster. Cormac Cas is the progenitor of the clan known as the Dal Cais or Dalcassians, translated to mean descendants of Cas. They were a minor clan of Ireland and ruled the northern section of Munster Province known as Thomond (all County Clare, southern Galway and northern Limerick, northwest Tipperary), while their cousins, the Eugenians (McCarthys and O’Sullivans) ruled the south of Munster known as Desmond. The kingship of Munster switched between these two clans every other generation. Two great families came from the Dalcassian Clan: The O’Briens and the O’Kennedys. Cinneidigh (Kennedy), King of Thomond, died in 954 A.D. He was succeeded by his son Brian, his 12th son. In time Brian rose in power and gained the kingship of Munster, obtained the allegiance of the other five provincial kings of Ireland, and eventually became High King of Ireland. Because he exacted tribute, his second name became Boru, meaning tribute. He is known as one of the greatest kings of Ireland, and in 1014 he defeated the Vikings (the other side of the family) at Dublin at the age of 88.