GUILLAUME [I] de Chaumont, son of OSMOND [I] de Chaumont & his wife --- (-[before 13 Apr 1175]). "Guillelmus de Caluimonte" was son-in-law of Louis VI King of France according to Orderic Vitalis, who says that he was captured while trying to take the castle of Tillières in 1119 and ransomed for 200 marks of silver[2150]. "Guillelmus filius Osmundi de Calvo Monte", who had married "filiam Ludovici regis", donated property to Chartres Saint-Père by charter dated 9 Apr 1119, which records "…Gaulterius de Monte Falconis, Haimo filius eius" as present[2151].Orderic Vitalis records that in 1137 King Stephen destroyed "munitionem Chitreii...spelunca latronum" [castle of Guitry, den of thieves] and "Guillelmus de Calvimonte cum Odmundo filio suo" rebelled[2152]. "...Willelmus filius Osmundi..." subscribed the charter dated to before 1151 under which Hugues Archbishop of Rouen granted "ecclesiam...Virginis Mariæ...Maldestor" to Pontoise Saint-Martin[2153].
m ([1114/17]) ISABELLE, illegitimate daughter of LOUIS VI King of France & his mistress Marie de Breuillet (after [1101/04] before 1108-5 Aug, after 13 Apr 1175). Louis VI King of France donated property to Chartres Saint-Père when "filiam meam" married "Willelmo, Othmundi filio", and now confirmed the donation, by charter dated 6 Jan 1118[2154]. "Isabel de Calvo Monte" donated property to Chartres Saint-Père by charter dated 1175 for the souls of "patris mei Lugdovici…regis Francorum…et…Willelmi filii Osmondi et Rainaldi de Braileic", with the consent of "filiorum meorum", subscribed by "Lugdovici filii eius, Philippi clerici, Gasthonis militis, Baudrici militis, Hugonis militis, Osmundi militis"[2155]. The necrology of Saint-Père-en-Vallée records the death "Non Aug" of "Isabella nobilis matrona de Calvomonte"[2156].
Guillaume & his wife had seven children