Essonne's a French department in the region of Île-de-France. It's named after the Essonne River. It was formed on 1 January 1968 when Seine-et-Oise was split into smaller departments. History The Essonne department was created on 1 January 1968, from the southern portion of the former department of Seine-et-Oise. In 1969, the communes of Châteaufort and Toussus-le-Noble were separated from Essonne and added to the department of Yvelines. Geography Essonne belongs to the region o… (More on Essonne)