Fleury-Mérogis is a commune in the Essonne department in northern France, in the southern suburbs of Paris. The commune has the Fleu…Fleury-Mérogis is a commune in the Essonne department in northern France, in the southern suburbs of Paris. The commune has the Fleury-Mérogis Prison, France's and Europe's largest prison. Inhabitants of Fleury-Mérogis are known as Floriacumois.