Essonne is a department in the southern part of the Île-de-France region in Northern France. It is named after the river Essonne. In 2019, it had a population of 1,301,659, across 194 communes. Essonne was formed on 1 January 1968, when Seine-et-Oise was split into smaller departments. Its prefecture is Évry-Courcouronnes. Its INSEE and postcode number is 91.