Baronscourt and its surrounding demesne are located on lands that originally belonged to a senior-ranking branch of the Ó Néill (English: O'Neill) clan,[2] a powerful and wealthy Gaelic royal family that ruled Tír Eoghain (Tyrone), a túath or Gaelic kingdom in Ulster.
The senior-ranking line of the Ó Néill clan of Tír Eoghain were the leading family within the wider Cenél nEógain dynastic group.
[3] The particular branch of the Ó Néill dynasty that dominated the north-western swathe of Tír Eoghain had several 'castles' or towerhouses, including one that was located on Island McHugh, a crannóg situated in what is now known as Lough Catherine, a short distance to the north of the current Baronscourt.
[2][4] Most of the Ó Néill dynasty had their lands confiscated by the English Crown in the early seventeenth century, shortly after the end of the Nine Years' War.
Sir George, a Catholic and a younger brother of the 1st Earl of Abercorn,[5] proceeded to have Derrywoone Castle built on these lands as his chief residence.
[2][6] The castle and its surrounding village were built just to the east of Lough Catherine and a short distance to the north-east of the later Baronscourt.
The house is seven bays wide and three stories high with a loggia of coupled Tuscan columns and a rotunda at the centre of the plan.
The agent of the 1st Marquess of Abercorn described the alterations as: "He just reverses the house, what was the backside is to be the entrance, and the front part of the rere.