Posen-West Prussia
Following the dissolution of West Prussia after World War I and the Treaty of Versailles, the Schlochau district became part of Schneidemühl Region in the newly established Frontier March of Posen-West Prussia province. The northeastern part of the district was transferred to the Second Polish Republic. When Posen-West Prussia was dissolved on 1 October 1938, the Schlochau district was transferred to Province of Pomerania and formed part of its new Frontier March of Posen-West Prussia region, which was actually the Schneidemühl Region enlarged by four previously Brandenburgian and Pomeranian districts and renamed as "Posen-West Prussia Region" for reasons of tradition. On 1 January 1939, the district was renamed from Kreis Schlochau to Landkreis Schlochau, in the course of uniforming the administrative terminology in all the states of Germany.