Original: Argenteuil is the second most populous commune in the suburbs Paris (after Boulogne-Billancourt) and by far the most populous commune in the Val-d'Oise department, although it is not its prefecture, which is shared between the communes of Cergy and Pontoise.
Simplified: Argenteuil is the second most populated town in the suburbs of Paris (after Boulogne-Billancourt) and the most populated commune in the Val-d'Oise department; however it is not the prefecture.