GUILLAUME [I] de Genève, son of AMEDEE [I] Comte de Genève & his first wife Mathilde de Cuiseaux ([1131/37]-25 Jul 1196). "Amedeus Gebennensis comes" donated property to the monastery of Abondance "in manu…consanguinei mei domini Bocardis ipsius ecclesiæ abbatis", for the souls of "patris mei Aymonis et matris meæ Itæ et Willelmi fratris mei et Matildis uxoris mæ" and for the protection of "filiorum meorum Wilelmi et Amedei", by charter dated 1153[871]. "Amedeus Gebennensium comes…et filius eius Guillelmus" restored the rights of the bishopric of Geneva, with the consent of "Amedeus quoque junior filius comitis", by undated charter[872]. Comte de Genève. "Willelmus…Gebennensis comes" founded the Chartreuse monstery of Pommiers, with the consent of "Humbertus filius meus…B. quoque uxor mea et filius meus Aymo quinquennis", by charter dated 1179[873]. A charter dated 1187 records an arbitration concerning the differences between "Wilielmum comitem Gebenn." and the bishop of Geneva[874]. "Wilermus Gebennensium et Valdensium comes" confirmed donations by "bonæ memorie predecessoris mei Aymonis [error for Amedei] comitis", with the consent of "Humbertus filius meus", by charter dated 1192, witnessed by "Turumbertus de Lucingio"[875].
m firstly AGNES de Savoie, daughter of AMEDEE III Comte de Savoie & his second wife Mathilde d'Albon (-before 1172). The death is recorded "Pridie Kal Aug" in 1194 of "dna Juliana abb.sa Sc.ti Andreæ", noting donations by "f.ris sui Humberti comiti Sabaudiæ" and "Agnetis sororis sue Gebennensis comitisse"[876].
m secondly BEATRIX de Faucigny, daughter of AIMON [I] Seigneur de Faucigny & his wife ---. "Willelmus…Gebennensis comes" founded the Chartreuse monstery of Pommiers, with the consent of "Humbertus filius meus…B. quoque uxor mea et filius meus Aymo quinquennis", by charter dated 1179[877]. Her parentage is confirmed by the Chronicle of Alberic de Trois-Fontaines which names her daughter "Margareta filia domni de Fusceneis de matre Guilelmi, filii Humberti comitis Gebenensis" as wife of "comitis Thome de Sabaudia"[878].
Guillaume [I] & his first wife had one child