William I of Geneva (c. 1132 – 25 July 1195) was Count of Geneva from 1178 to 1195, in succession to his father, Count Amadeus I of Geneva. William's mother was Amadeus' wife, Matilda de Cuiseaux.
He died at the Château de Novel in Annecy.
- His first wife was Marguerite Beatrice de Faucigny, by whom he had three children:
- Humbert of Geneva
- Marguerite of Geneva, wife of Thomas I of Savoy
- William II of Geneva
- His second wife was Agnes of Savoy, daughter of Amadeus III of Savoy, by whom he had one daughter:
- His third marriage, to Beatrice de Vaupergue, was childless.
- In 1195 William was escorting his daughter Marguerite to France for her intended wedding to King Philip II. Thomas of Savoy ambushed the party, carried off Marguerite and married her himself, producing some eight sons and six daughters.