Originally written in a Gaelic form as Mag Oireachtaigh (or MacGeraghty in English), the name is derived from the word oireachtach, referring to a member of an assembly.
The name of the modern national legislative body in Ireland, the Oireachtas comes from the same Gaelic root.
The MacGeraghty clan are descended from the Siol Muireadaigh of the Kingdom of Connacht, the same Gaelic lineage and homeland as the Ó Conchubhair dynasty.
They were rulers of Clann Tomaltaigh and the Muintir Roduib[1][2] and are referred to in the topographical poem Tuilleadh feasa ar Éirinn óigh by Giolla na Naomh Ó hUidhrín.
A Chief of the name, called McGiriaght is listed in the Composition Book of Connacht in 1585, as seated in the Barony of Athlone.