Isabelle de Grandson

Isabelle de Grandson (born c. 1310) was the daughter of Peter II de Grandson, lord of Belmont, and Blanche of Savoy-Vaud. She married Louis I de Cossonay, lord of Cossonay in the Vaud, binding two leading Vaudois dynasties to Savoy.

Her children included John III, later lord of Cossonay, Louis III, the family's last male, and Girard of L'Isle. When Louis I died before 1333, their uncle Aymon tutored the children. Long widowed, she willed them her estates in 1366.