George John Frederick Sackville, 4th Duke of Dorset (15 November 179314 February 1815), styled Earl of Middlesex until 1799, was a British nobleman.
The only son of John Sackville, 3rd Duke of Dorset, and his wife Arabella Cope (a daughter of Sir Charles Cope, Bt.). After his father's death, his mother married Charles Whitworth, 1st Earl Whitworth.
He was educated at Harrow and Christ Church, Oxford, receiving an MA from the latter on 30 June 1813.
He was appointed High Steward of Stratford-on-Avon and was commissioned as a captain in the Sevenoaks and Bromley Regiment of Local Militia on 27 April 1813[1] and on 26 July the same year he was promoted to Lieutenant-Colonel Commandant of the regiment.[2]
Lord Dorset died in February 1815, of a fall from his horse while hunting on Killiney Hill in County Dublin. He had no children, so he was succeeded as duke by his first cousin once removed, Charles Sackville-Germain. His estate of Knole passed to his sister Elizabeth Sackville-West, Countess De La Warr.
At the time of his death he had just become engaged to Lady Elizabeth Thynne (born 1795), elder daughter of Thomas Thynne, 2nd Marquess of Bath. (She went on to marry October 1816 Lord Cawdor and have many children).[3]