The western portion of the district remained in Germany and became part of the Frontier March of Posen-West Prussia until 1938.

On 1 July 1922 the new Prussian province of Grenzmark Posen-West Prussia was formed, which included the Flatow district.

[3] The Sturmabteilung, Schutzstaffel, Hitler Youth and Bund Deutscher Osten launched attacks on Polish institutions, schools and activists.

[7] During the German invasion of Poland, which started World War II in September 1939, persecution further intensified with mass arrests of Polish activists, who were detained in temporary camps in Lipka and the neighbouring city of Piła, and then deported to concentration camps, as well as expulsions and closure of Polish schools and enterprises.

[8] During the war, the Germans operated several forced labour subcamps of the Stalag II-B prisoner-of-war camp in the district.

After the end of World War II, the district became again part of Poland under the terms of the Potsdam Agreement.