GUILLAUME [I] de Nevers, son of RENAUD I Comte de Nevers & his wife Hedwige de France (-20 Jun 1098, bur Nevers, Saint-Etienne). "Rainaldus comes Nivernensis" donated property "Belmontis" to Cluny, for the souls of "…uxoris mee Advise et filiorum meorum qui presentes sunt…" by charter dated to [1028/40], subscribed by "filii eorum Willelmi"[2439]. He succeeded his father in 1040 as Comte de Nevers et d'Auxerre. Comte de Tonnerre, de iure uxoris. "Willelmus Nivernensis comes" made a donation to Cluny dated 13 Dec 1097[2440]. The Annales Nivernenses record the death in 1098 of "Willelmus comes Nivernesium"[2441]. The necrology of the abbey of Saint-Denis records the death "XII Kal Jul" of "Guillelmus comes Nivernensis"[2442].
m firstly ([1039]) ERMENGARDE Ctss de Tonnerre, daughter of RENAUD [I] Comte de Tonnerre & his wife Helvis --- ([1023/26]-before 1090). "Milo comes Tornodorensis castri" donated property to the monastery of Saint-Michel, for the soul of "filii mei Othonis" buried in the monastery and "uxore mea Herviz…filio nostro Arduyno ac filia Ermengarda", by charter dated Jul 1036[2443]. Her birth date is estimated from her marriage in [1039], combined with the fact that she was still not of marriageable age in 1036. "Raynardus comes" donated property to the monastery of Saint-Michel (on his deathbed), with the consent of "uxoris mee Herviz et filii mei Harduini sive filie mee Ermengarde", by charter dated 16 Jul 1039 which also names "mater mea Ermengardis"[2444]. Her marriage is referred to in the Gesta pontificum Autissiodorensium[2445]. She succeeded as Ctss de Tonnerre in 1065 when her cousin Comte Hugues-Rainard became bishop of Langres[2446].
m secondly (before 1085) MATHILDE, daughter of ---. The primary source which confirms her marriage has not yet been identified.
Comte Guillaume [I] and his first wife had five children