He was the son of Count Raoul III de Vexin and Adèle of Bar-sur-Aube. Simon was brought up at the court of William of Normandy, and inherited his father"s sizable lands in 1074 These lay between the royal domain of King Philip I of France and the lands of William of Normandy, by then King of England, and made Simon an important manitoba
He is also known as Simon de Vexin and Saint Simon. In the meantime, King Philip attempted to withhold part of Simon"s inheritance and a three-year-long war resulted. A marriage with Adela was within the prohibited degree of consanguinity and Simon went to Rome to meet with Pope Gregory VII, perhaps to arrange a dispensation.
Whether this was his motive, the Pope arranged a truce between Simon and King Philip.
Perhaps as part of the papal settlement, Simon married a daughter of the Count of Auvergne (chronologically, this would have been either William V or Robert II) in around 1075. Simon was not content with the relatively luxurious surrounds of the Abbey of Saint-Claude, and decided upon a life as a hermit in the forests of Burgundy on the upper reaches of the Doubs River.
There he and a few colleagues constructed cabins and cleared land to farm. This priory remained dependent upon Sainte-Claude until the 12th century, then upon Saint-Oyen de Joux.
The village of Mouthe later grew up around the priory.
Simon undertook a pilgrimage to the Holy Land, and then again to Rome where he died. He received the Last Rites from Gregory VII. Simon was later beatified and his relics are still kept at Mouthe where a statue in his honour was erected in 1934.
