From the Wikipedia page 
The Communauté d'agglomération Roissy Pays de France is a communauté d'agglomération in the Val-d'Oise and Seine-et-Marne départements and in the Île-de-France région of France. It was formed on 1 January 2016 by the merger of the former communauté d'agglomération Val de France, communauté d'agglomération Roissy Porte de France and 17 communes that were part of the Communauté de communes Plaines et Monts de France. Its seat is in Roissy-en-France. Its population was 349,490 in 2014, of which 2,881 in Roissy-en-France and 57,455 in Sarcelles, the largest commune of the communauté d'agglomération.