Guillaume DE BLOIS comte de Chartres
- Born: Abt 1078, Blois, Loir-et-Cher, Centre, France
- Died: Abt 1150
His parentage is stated by Orderic Vitalis, who names him first in order of the sons which he lists, specifying that his father-in-law was Gilo de Sully, and calling him a "good and peaceful man blessed with children and wealth". Orderic also provides some indication of his birth year when he records that his mother Ctss Adela provided troops to Louis VI King of France at the time of the siege of Montmorency in  "because Count Stephen her husband had gone on crusade and her eldest sons, William and Theobald, who were not yet of age, were unable to command troops of knights". The description is confused because Count Etienne had died several years earlier, but it nevertheless provides some indication of the comparative youth of the brothers Guillaume and Thibaut at the time. "Henricus comes cognomina Stephanus necnon et Adela uxor eius cum filiis nostris" granted immunities to Chartres Notre-Dame by charter dated [Oct 1100/1101], signed by "Stephani comitis, Adele comitisse, Guillelmi, Stephani, Odonis, Teobaldi". Comte de Chartres. Sire de Sully, by right of his wife. He was disinherited, retaining only Sully. According to Weir, Guillaume is described in the chronicles as an idiot but she does not cite the primary source. During a dispute in  with the chapter of Chartres that was awaiting arbitration, he forced the burgesses of Chartres to form a confederation and take a solemn oath to kill the bishop. Chibnall, in order to reconcile this incident with the description of Guillaume by Orderic Vitalis, speculates that he was of retarded mental development and, though irresponsible, violent only in words.
Guillaume married Agnès DE SULLY, daughter of Seigneur Gilles (Gilon) I DE SULLY and Vctse Eldeberge DE BOURGES. (Agnès DE SULLY was born about 1080 in Sully, Saone-et-Loire, Bourgogne, France and died after 1098.)