William de Reviers, 5th Earl of Devon (died 10 September 1217) was the son of Baldwin de Redvers, 1st Earl of Devon and Adelise Baluun. William de Redvers is also William de Vernon, because he was brought up at Vernon Castle, in Normandy, the seat of his grandfather.
He took part in Richard the Lionheart's second coronation, in 1194, when the Canopy was supported by four Earls; he consistently supported King John. Nevertheless, at the end of John's life, the King permitted Falkes de Breauté, one of his mercenary captains to seize the Earl's widowed daughter-in-law, force a marriage, and grab her dowry. These events are also featured in the novel Leopards and Lilies by Alfred Duggan.
On his death his title passed to his grandson Baldwin de Redvers, 6th Earl of Devon, his only son having died.
He was married to Mabile de Beaumont, daughter of Robert de Beaumont, Count of Meulan and granddaughter (on her mother's side) of Reginald, Earl of Cornwall and had children:
| Preceded by Richard de Redvers, 4th Earl of Devon |
Earl of Devon 1193–1217 |
Succeeded by Baldwin de Redvers, 6th Earl of Devon |