William Parr, 1st Marquess of Northampton, 1st Earl of Essex and 1st Baron Parr, KG (14 August 1513 – 28 October 1571) was the son of Sir Thomas Parr and his wife, Maud Green, daughter of Sir Thomas Green, of Broughton and Greens Norton.
William Parr was brother of the Queen consort, Catherine Parr, the sixth and final wife of Henry VIII, and of Anne Parr.