 William O'Brien, 4th Earl of Inchiquin

William McWilliam O'Brien, 4th Earl of Inchiquin, KB, PC(I) (1700 – 18 July 1777) was an Irish peer and Whig politician who sat in the House of Commons between 1722 and 1754.O'Brien was the eldest son of William O'Brien, 3rd Earl of Inchiquin, and his wife, Mary (née Villiers), sister of the 1st Earl of Jersey, and inherited his father's titles in 1719.