John III de Cossonay

John III de Cossonay (died before 1369), lord of Cossonay and L'Isle, was the eldest son of Louis I de Cossonay and Isabelle de Grandson. Knighted young, he pilgrimaged to the Holy Land and in 1343 married Louise of Montbéliard, daughter of Count Henry.

In 1348 he signed a mutual inheritance treaty with his cousin the lord of Varembon, and in 1357 confirmed Cossonay's town franchises. He died before July 1369, leaving his son Louis II to succeed him.