Mary O'Brien, 3rd Countess of Orkney

Scottish noble (1721–1791)

Parents

• Anne O'Brien, 2nd Countess of Orkney
• William O'Brien, 4th Earl of Inchiquin

Children

• Mary FitzMaurice, 4th Countess of Orkney

Siblings

• Murrough O'Brien
• Augustus O'Brien
• George O'Brien
• William O'Brien

Partners

• Murrough O'Brien, 1st Marquess of Thomond