Henrietta Harley, Countess Of Oxford And Countess Mortimer

Henrietta Harley, Countess of Oxford and Countess Mortimer (born Lady Henrietta Cavendish Holles) was an English noblewoman born on 11 February 1694. She was the sole child and heiress of John Holles, 1st Duke of Newcastle, and his wife, Lady Margaret Cavendish, daughter of Henry Cavendish, 2nd Duke of Newcastle-upon-Tyne.

Throughout her youth, Henrietta's marriage prospects were subjects of interest, with her alliances considered as strategic matches linked to her father's influence. In December 1703, a suitor was the Intendant of the Court of a Count of the Holy Roman Empire. In June 1706, the Elector of Hanover's son—later King George I of Great Britain—also sought her hand. Between 1707 and 1711, she was proposed to Lord Hertford, the son of the Duke of Somerset. In 1709, Count Nassau expressed interest, and in 1711, Lord Danby, grandson of Thomas Osborne, 1st Duke of Leeds, was among her suitors.

Ultimately, her father arranged her marriage to Edward Harley, 2nd Earl of Oxford and Earl Mortimer. The marriage took place on 31 August 1713 at Wimpole Hall. Through her inheritance, Henrietta brought significant estates into the marriage, including Welbeck Abbey in Nottinghamshire, Bolsover Castle, and Wimpole Hall in Cambridgeshire.

Henrietta and Edward Harley had two children. Their son, Henry Cavendish Harley, Lord Harley, was born in 1714 but died after only four days. Their only surviving child to reach maturity was Margaret (1715–1785), who inherited most of the Holles-Harley estates upon her parents' deaths.

The Harley family's influence extended into geographical naming; Henrietta Place (formerly Henrietta Street) in Marylebone, Westminster, was named after her. Nearby Harley Street, known for housing numerous medical specialists, was named after her husband. The broader area, including streets such as Oxford Street, Wigmore Street, and Wimpole Street, was developed during the Harley family's ownership.

Henrietta Harley died on 9 December 1755 and was buried on 26 December 1755 in the vault of the Duke of Newcastle in Westminster Abbey.