Mary O'Brien, 3rd Countess of Orkney

Mary O'Brien, 3rd Countess of Orkney (c. 1721 – 1790) was the eldest daughter of Anne O'Brien, 2nd Countess of Orkney, and William O'Brien, 4th Earl of Inchiquin, and Countess of Orkney in her own right.

Mary O'Brien, 3rd Countess of Orkney

Mary O'Brien, 3rd Countess of Orkney (c. 1721 – 1790) was the eldest daughter of Anne O'Brien, 2nd Countess of Orkney, and William O'Brien, 4th Earl of Inchiquin, and Countess of Orkney in her own right.