Communauté d'agglomération Plaine Vallée is the communauté d'agglomération, an intercommunal structure, covering northwestern suburbs of Paris. It is located in the Val-d'Oise department, in the Île-de-France region, northern France. It was created in January 2016. Its seat is in Montmorency. Its area is 74.1 km2. Its population was 182,585 in 2018.