Sir William Courtenay (c. 1529 – 29 September 1557) was a landowner in Devon. He was the son of George Courtenay (died 1533), who predeceased his own father, by his wife Catherine St Ledger, daughter of Sir George St Ledger of Annery. He succeeded his grandfather Sir William Courtenay (1477 – 1535), of Powderham in 1535. He was knighted in 1553 and elected to Parliament for Plympton in 1555.
On 28 Nov 1545, he married Elizabeth Paulet (c. 1536 – 4 Nov. 1576), daughter to John Paulet, 2nd Marquess of Winchester, by whom he had two children: Jane, born 1551, and his heir, William (1553 – 24 June 1630). He took part in the battle of St. Quentin in August 1557 in Picardy, France, and died on 29 September 1557.
In 1831, a decision of the House of Lords determined that he had succeeded his sixth cousin once removed (Edward Courtenay, 1st Earl of Devon) as de jure 2nd Earl of Devon in 1556.