William I, Count of Nevers (French: Guillaume Ier, c. 1029 – 20 June 1100), was the son of Renauld I, Count of Nevers and Hedwig of France, Countess d'Auxerre. He married Ermengarde, daughter of Renauld, Count of Tonnerre about 1039. William died in 1098.
William I and Ermengarde had:
Renauld II (d. 1089), succeeded his father as Count of Nevers and Count of Auxerre.
William II, succeeded his father as Count of Tonnerre
Robert (d. 1095), later Bishop of Auxerre
Ermengarde (d. 1090–95), married Hubert de Beaumont-au-Maine, Viscount of Maine
Helvise, married William, Count of Évreux