Ardèche is a department in Auvergne-Rhône-Alpes, Southeastern France. It is named after the river Ardèche and had a population of 328,278 a…Ardèche is a department in Auvergne-Rhône-Alpes, Southeastern France. It is named after the river Ardèche and had a population of 328,278 as of 2019. Its prefecture is in Privas, but its largest city is Annonay.