O’Rourke, Tiernan, prince of Brefny, [39], [46], [47], [49]
O’Rourkes, the, of Brefny (Brefny-O’Rourke was Leitrim with Tullyhaw and Tullyhunco in Cavan), [63], [140], [239], [266]
Osbertstown, [240]
O’Sealbhaigh, Augustine, Bishop of Waterford, [35], [52]
O’Shaughnessy, seated at Gort in Galway, [271], [410]
— Sir Dermot, [333]
Osney, [198]
Ossory, Ossorians, [43], [47], [81]
— Earldom;