|Date of birth|
|Date of death||1109|
Guy III Trousseau (died 1109) was lord of Montlhéry. He was the son of Milo I of Montlhéry and Lithuise, and the elder brother of Milo II of Montlhéry. .
Guy had the temperament of a warrior, and went on the First Crusade in 1096. He was one of those who deserted the army during the Siege of Antioch (along with his grandfather, Stephen, Count of Blois), and did not dare return directly to France, instead returning home by a long detour through Epirus and Italy.
He had only one child:
- Elizabeth of Montlhéry. In 1103 Elizabeth married Philip, Count of Mantes, son of Philip I of France and Bertrada de Montfort.