As a result of the Treaty of Versailles following World War I, most of West Prussia, including much of the Marienwerder Region, was allocated to the Second Polish Republic. Parts of the territory east of the river Vistula took part in the East Prussian plebiscite and remained in the Free State of Prussia within Weimar Germany. These parts of the Marienwerder Region were officially incorporated into the Province of East Prussia in 1922, and renamed from Marienwerder Region to Region of West Prussia. This smaller region consisted of the rural districts of Elbing-Land [de], Marienburg in West Prussia [de], Marienwerder, Rosenberg in West Prussia, Stuhm, and the city of Elbing (Elbląg); the districts of Elbing and Marienburg and the city of Elbing had previously been part of the Danzig Region. The districts of Deutsch-Krone, Flatow, and Schlochau became part of the new Prussian Frontier March of Posen-West Prussia. The districts of Graudenz, Konitz, Culm, Löbau, Schwetz, Strasburg in West Prussia, and Thorn became part of the Pomeranian Voivodeship of Poland.
On 26 October 1939, following the Wehrmacht's conquest of the Polish Corridor at the beginning of World War II, the Region of West Prussia was transferred from East Prussia to the newly created Reichsgau Danzig-West Prussia. It was also given back its original name of Marienwerder Region and included besides of German districts also occupational district authorities on Polish territory.
The region was dissolved in 1945 following Nazi Germany's defeat in the war. The Soviet conquerors handed the region's territory to Poland in March 1945. Since that time it has been part of Poland. At the Potsdam Conference, the three Allies assigned the region to Polish administration in August 1945, and the German-Polish Border Treaty confirmed the annexation in 1990.