William O'Brien, 3rd Earl of Inchiquin

William O'Brien, 3rd Baron O'Brien of Burren, 8th Baron & 3rd Earl of Inchiquin PC (1662 – 24 December 1719) was an Irish nobleman.

He married his cousin Mary Villiers, daughter of Sir Edward Villiers of Richmond and Frances Howard, the youngest daughter of Theophilus Howard, 2nd Earl of Suffolk and Elizabeth Hume.

Like his father, he was attainted in his absence by the Irish Parliament of King James II in 1689.

He was Privy Councillor to Queen Anne and King George I, Colonel of Foot in 1703 and Mayor of Kilkenny from 1704 to 1705.

Children of William O'Brien, 3rd Earl of Inchiquin and Mary Villiers:

William O'Brien, 3rd Earl of Inchiquin
Mary, née Villiers, daughter of Sir Edward Villiers, and sister of the 1st Earl of Jersey, married William, 3rd Earl of Inchiquin. On her wedding Queen Mary, to whom she had been a Maid of Honour, provided a wedding supper at Kensington Palace in London, plus £4,000 in cash and £1,000 in clothing and jewellery.