William de Mandeville, 3rd Earl of Essex (1st Creation) (died 14 November 1189) was a loyal councillor of Henry II and Richard I of England.
On the death of his elder brother Geoffrey late in 1166, he returned to England and became Earl of Essex, where he spent much time at the court of Henry II.
Philip attempted to intervene in the court politics of the Kingdom of Jerusalem but was rebuffed, and the two fought for the Principality of Antioch at the siege of Harim.
Geoffrey contracted to pay an unprecedentedly large relief for the Mandeville inheritance, but he rapidly fell into arrears.
The king awarded the Mandeville estates and, eventually, the earldom of Essex to Geoffrey Fitz Peter by right of his wife.