Duke of Grafton is a title in the Peerage of England. It was created in 1675 by Charles II of England for Henry FitzRoy, his second illegitimate son by the Duchess of Cleveland. The most notable duke of Grafton was Augustus FitzRoy, 3rd Duke of Grafton, who served as Prime Minister from 1768–1770.
The Duke of Grafton holds three subsidiary titles, all created in 1672 in the peerage of England: Earl of Euston, Viscount Ipswich, and Baron Sudbury. Between 1723 and 1936 the dukes, being descended from the 1st Duke's wife Isabella FitzRoy, 2nd Countess of Arlington, also held the titles Earl of Arlington, Viscount Thetford, and Baron Arlington. Those titles fell into abeyance between the 9th Duke's sisters, with the abeyance of the barony of Arlington ending in 1999.