Roer is the name of a département of the First French Empire in present day Germany and the Netherlands. It was named after the river Rur, which flows through the département. It was formed in 1795, when the Southern Netherlands and the left bank of the Rhine were occupied by the French. The département de la Roer was formed from the duchies of Jülich and Cleves, the part of the Archbishopric of Cologne left of the Rhine, the free city of Aachen, the Prussian part of the duchy of Guelders and some smaller territories. In 1805 the city Wesel was added to the département.
- Aachen, cantons: Aachen (2 cantons), Burtscheid, Düren, Eschweiler, Froitzheim, Geilenkirchen, Gemünd, Heinsberg, Linnich, Monschau and Sittard.
- Cleves, cantons: Cleves, Geldern, Goch, Horst, Kalkar, Kranenburg, Wankum, Wesel and Xanten.
- Krefeld, cantons: Krefeld, Bracht, Erkelenz, Kempen, Moers, Neersen, Neuss, Odenkirchen, Rheinberg, Uerdingen, Viersen
- Cologne, cantons: Cologne (4 cantons), Bergheim, Brühl, Dormagen, Elsen, Jülich, Kerpen, Lechenich, Weiden and Zülpich.
Its population in 1812 was 631,094.
After Napoleon was defeated in 1814, the département was divided between the United Kingdom of the Netherlands (left bank of the Meuse and a strip along its right bank including Gennep, Tegelen and Sittard, in present Dutch Limburg) and the Kingdom of Prussia (Province of Jülich-Cleves-Berg, presently part of North Rhine-Westphalia, Germany).