Henrietta Harley, Countess of Oxford and Countess Mortimer

Henrietta Harley (née Holles), Countess of Oxford and Countess Mortimer (11 February 1694 – 9 December 1755) was an English noblewoman, the only child and heiress of John Holles, 1st Duke of Newcastle and his wife, the former Lady Margaret Cavendish, daughter of Henry Cavendish, 2nd Duke of Newcastle-upon-Tyne.

Her hand was sought in marriage even in her youth, as a means of alliance with her powerful father. Suitors included the Intendant of the Court of a Count of the Holy Roman Empire in December 1703, the Elector of Hanover's son (later George I of Great Britain) in June 1706, the Duke of Somerset's son Lord Hertford in 1707–11, Count Nassau in 1709, and finally Lord Danby (grandson of Thomas Osborne, 1st Duke of Leeds) in 1711, before her father settled on Edward Harley, 2nd Earl of Oxford and Earl Mortimer. They were married on 31 August 1713, at Wimpole Hall. She brought, through inheritance, Welbeck Abbey in Nottinghamshire and Wimpole Hall in Cambridgeshire to her husband.

They had two children. Their son, Henry Cavendish Harley, Lord Harley, lived only four days. Their only child to attain maturity was Margaret (1715–1785), and so whilst Margaret inherited most of the combined Holles-Harley fortunes on her parents' deaths, the title of Earl of Oxford and Earl Mortimer passed to Edward's cousin (also Edward).

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