Knockninny is believed to takes its name from St. Ninnidh, a 6th-century saint. St. Ninnid is listed as one of the "twelve apostles of Ireland", and bore the epithet of Saobhruisc meaning "squinting", given rise to the names; "the squinting saint" or "one-eyed saint".[3] The hill of St. Ninnid lies on the southern shore of Upper Lough Erne.[4]
Before 1450 there is no mention of this barony's name, however the land is noted as being an early Maguire stronghold, with a MacManus (Irish: Mac Maghnuis) sept of Clan Maguire centered here.[3][4]