William Cavendish, 1st Earl of Devonshire (27 December 1552 – 3 March 1626) was an English nobleman, politician, and courtier.
The second son of Sir William Cavendish and Bess of Hardwick, he was educated with the children of George Talbot, 6th Earl of Shrewsbury, whom his mother married after his father's death. She made him a rich allowance in his youth. He then entered Clare College, Cambridge.
He was M.P. for Liverpool in 1586 and Newport (Cornwall) in 1588. He was appointed High Sheriff of Derbyshire, where the estates of his family lay, for 1595 and Justice of the Peace in 1603. He was created Baron Cavendish of Hardwick in 1605, thanks to the representations of his niece, Arbella Stuart.
He participated in the colonisation of the Bermudas, and Devonshire Parish was called after him; he also was a supporter of colonising Virginia.
His mother's death in 1608, and his elder brother Henry's death in 1616, gave him a vast fortune. He was in attendance on James I in a progress in Wiltshire in 1618, and on 2 August was created Earl of Devonshire, while the court was staying at the Bishop of Salisbury's palace; he was reported to have paid £10,000 for the title. He died on 3 March 1626, and was buried at St Peter's Church, Edensor. The 1st Earl of Devonshire and his brother Henry (died 1616) are commemorated through the Cavendish Memorial inside the church, a magnificent early-17th-century church monument.