Milly-la-Forêt is a commune in the Essonne department in the Île-de-France region in northern France. The Forest of Fontainebleau, in th…Milly-la-Forêt is a commune in the Essonne department in the Île-de-France region in northern France. The Forest of Fontainebleau, in the western end of which Milly-la-Forêt lies, is composed of the Oligocene Fontainebleau sands, which are a marine deposit, laid down in an intertidal zone.