William de Greystoke, 2nd Baron Greystoke

William de Greystoke, 2nd Baron Greystoke, (6 January 1321 – 10 July 1359) of Greystoke in Cumbria, was an English peer and landowner.

Greystoke was the son of Ralph de Greystoke, 1st Baron Greystoke, and his wife Alice, daughter of Hugh, Lord Audley.

He was born at the family home in Grimthorpe, on 6 January 1321. Greystoke's father died while he was still a child and he became a ward of his mother's second husband, Ralph Neville, 2nd Baron Neville de Raby, until he reached his majority in 1342. During the next ten years he was involved, on the English side, in the Hundred Years' War between the Kingdom of England and the Kingdom of France and was present at the Siege of Calais in 1346. He served under Edward, the Black Prince, in France. He participated in the Northern Crusades of Henry of Grosmont, 1st Duke of Lancaster to Prussia in 1351–2. In the early 1350s he was involved in the negotiations to secure the release of King David II of Scotland, who had been taken prisoner at the Battle of Neville's Cross on 17 October 1346. Greystoke was made a captain of Berwick-upon-Tweed, but due to his service in France, he was not present when the town fell to the Scots in August 1355. In October 1353 Greystoke received a royal licence to crenellate "his dwelling place", later known as Greystoke Castle. He was also responsible for renovations on Morpeth Castle which he also owned.