The name O’Reilly and its variations Reilly and Riley come from the Gaelic O Raghallaigh, which meant gregarious. They were from the Kingdom of Beffny which was part of Counties Cavan and Longford where they were long the leading family. The O’Reilly’s were very strong supporters of the church. Cathal O Raghallaigh Prince of Beffny founded the Lough Oughter Monestary in 1237. There were many O’Rilley Abbotts and several Bishops between the 11th and 16th century.