Frances Sidney, Countess of Sussex

Frances Radclyffe (née Sidney), Countess of Sussex (1531–1589) was a Lady of the Bedchamber to Queen Elizabeth I and the founder of Sidney Sussex College, Cambridge.

She was the daughter of Sir William Sidney, of Penshurst Place in Kent, a prominent courtier during the reign of King Henry VIII, and his wife, the former Anne Packenham. She was the sister of Sir Henry Sidney, and the aunt of both the poet Sir Philip Sidney and the first Sidney Earl of Leicester.

In 1555, she married (as his second wife) Thomas, Viscount FitzWalter, who was appointed Lord Deputy of Ireland in 1556 and who succeeded his father as 3rd Earl of Sussex in 1557. They left no children.

In her will, Lady Sussex left the sum of £5,000 together with some plate to found a new college at Cambridge University 'to be called the Lady Frances Sidney Sussex College'. Her executors, Sir John Harington and Henry Grey, 6th Earl of Kent, supervised by Archbishop John Whitgift, founded the college seven years after her death. The mascot of the college is the blue and gold porcupine, taken from the Sidney family coat of arms.