William Stanley, 6th Earl of Derby (1561 - 29 September 1642) was an English nobleman.
He was a son of Henry Stanley, 4th Earl of Derby and Lady Margaret Clifford. His mother was heiress presumptive of Elizabeth I of England from 1578 to her own death in 1596.
His maternal grandparents were Henry Clifford, 2nd Earl of Cumberland and Lady Eleanor Brandon. Eleanor was the third child of Charles Brandon, 1st Duke of Suffolk and Mary Tudor. Mary was the fifth child of Henry VII of England and Elizabeth of York.
He married Elizabeth de Vere, daughter of Edward de Vere, 17th Earl of Oxford and Anne Cecil. The latter's maternal grandparents were William Cecil, 1st Baron Burghley and his second wife Mildred Cooke. Mildred was the eldest daughter of Anthony Cooke and his wife Anne Fitzwilliam. They had five children:
