Guillaume DE BLOIS, Comte de Chartres, Seigneur de Sully
- Born: Between 1090 and 1093, Blois, Loir-et-Cher, Centre, France
- Died: Abt 1150
Orderic Vitalis records that “Stephanus Blesensis palatinus comes” and his wife had “filios quatuor: Guillelmum et Tedbaldum, Stephanumque et Henricum”, adding that Guillaume was “gener Geronis de Solleio et hæres” and “vir bonus...et pacificus, et sobole pollens atque facultatibus” (“a good and peaceful man, powerful through his descendants and his 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. Seigneur 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. The comment may be based on a letter of Ivo Bishop of Chartres which records that, during a dispute (dated by Chibnall to  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 ("good and peaceful man", quoted above), speculates that he was of retarded mental development and, although irresponsible, violent only in words. 1
Guillaume married Agnès DE SULLY, daughter of Seigneur Gilles (Gilon) I DE SULLY and Vctse Eldeberge DE BOURGES. (Agnès DE SULLY was born in Sully, Saone-et-Loire, Bourgogne, France.)