Marquess of Rockingham
The third Earl, William Fitzwilliam, also represented Peterborough in the House of Commons. In April 1742 he was created Lord Fitzwilliam, Baron of Milton in the County of Northampton, in the Peerage of Great Britain, and in 1746 he was further honoured when he was made Earl Fitzwilliam, of Norborough with the subsidiary title Viscount Milton, both in the County of Northampton, also in the Peerage of Great Britain. Lord Fitzwilliam married Lady Anne Watson-Wentworth (died 1769), daughter of Thomas Watson-Wentworth, 1st Marquess of Rockingham, and sister of Charles Watson-Wentworth, 2nd Marquess of Rockingham. He was succeeded by his son, the fourth Earl.