The O'hEochaidh sept
The Dál Fiatach were a group of related tribes located in north-east Ulster in the Early Christian and Early Medieval periods of the history of Ireland.
See the map below for Dál Fiatach.
The kingdom of Ulaid in the time of the Dál Fiatach was reduced from late pre-Christian times, when it had extended south and west to cover most of Ulster. By about 400, the kingdom included the lands which would become County Louth, County Down and County Antrim, as well as parts of Armagh and Tyrone. County Down was the centre of the Dál Fiatach lands, and the chief royal site and religious centre of the Dál Fiatach was at Downpatrick. In later times, from the 9th century, Bangor, originally controlled by the neighbouring Dál nAraidi, became the main religious site patronised by the kings.
The Dál Fiatach and their dependents were the Ulidians, the Red Branch of Ulster. Their ancestors ruled all of Ulster from Emain Macha, and they are the ones renowned in the Ulster Cycle, such as King Conchobhar (Conor) mac Nessa, CuChullain, Fergus and Sualtam mac Roth. They are featured prominently in the Cattle Raid of Cooley. They were displaced as rulers of all Ulster by the Ui Neill Clan, which invaded from Connaught and Meath. These were led by the Three Collas, who colonized Airghialla (Oriel). The Red Branch were left in control of Counties Antrim and Down, the Kingdom of the Ulaidh or Ulidia.
The descendants of this royal line include the septs O'Hoey and McDunleavy.
The O'hEochaidh sept , later anglicized as O'Hoey and Hoy, were noted chiefs of Uladh (pronounced 'Ullah') in the 10th century.
A sept is similar to the Scots clan. The sept was never a political grouping as the clan was, it was just all the members of one related group of people. It was similar to the Roman gens.
The name O'hEochaidh means descendant of Eochaidh (pronounced 'Owey'), which itself is derived from the Gaelic 'eachach' which means 'abounding in horses'. The Ui Eachach name on the map below left, shows the center of the O'hEochaidh lands.
By the time of the Norman Invasion in the late 12th century, the MacDonlevy sept, named for their late 11th cenury ancestor Donn Slébhe O'hEochaidh, were chiefs of Uladh having surpassed their kinsman the O'hEochaidh. The end of many centuries of Ulidian power came with the defeat of the MacDonlevys by the Normans in 1177.
After this, the name O'hEochaidh becomes less in Antrim and Down and very common in the neighboring counties of Louth, Armagh and Monaghan. The name is especially found in Louth and the parts of South Armagh and east Monaghan that adjoin it.