The Earldom of Darlington has been created twice, each time in the Peerage of Great Britain. The first time was in 1722 for the Countess of Kielmansegg, half-sister¹ of King George I. She was created Baroness Brentford at the same time. This creation was for life only, and so the titles expired on her death in 1730. The second creation was in 1754 for Henry Vane, 3rd Baron Barnard, along with the subsidiary title of Viscount Barnard. The 3rd Earl was created Marquess of Cleveland in 1827 and Duke of Cleveland in 1833. These titles, and the Earldom of Darlington, became extinct on the death of the 4th Duke (and 6th Earl) in 1891. The barony of Barnard remains extant.

Countess of Darlington, first creation (1722)

• Sophia Charlotte von Platen-Hallermund, Countess of Darlington (1675-1725)

Earls of Darlington, second creation (1754)

• Henry Vane, 1st Earl of Darlington (c. 1705-1758)
• Henry Vane, 2nd Earl of Darlington (1726-1792)
• William Henry Vane, 3rd Earl of Darlington, 1st Duke of Cleveland (1766-1842)
• Henry Vane, 4th Earl of Darlington, 2nd Duke of Cleveland (1788-1864)
• William John Frederick Vane, 5th Earl of Darlington, 3rd Duke of Cleveland (1792-1864)
• Harry George Powlett, 6th Earl of Darlington, 4th Duke of Cleveland (1803-1891)

Note

¹ Sophia has often, but erroneously, been asserted to have been mistress of King George I of Great Britain and Ireland: in fact, she was his half-sister. Court ‘observers’ were apparently unable to fathom that George I would have a woman among his intimates without being intimate with her. According to vol. 14 of the Complete Peerage: “The stories that Sophia Charlotte was mistress of George I were demolished in Ragnild Hatton, George I, Elector and King, 1879, pp. 23-4, 134-5.”