Sępólno County was invaded and annexed by Nazi Germany in 1939, and the town now became part of Landkreis Zempelburg, under the name "Vandsburg". During the German invasion, the "Einsatzgruppe IV" entered the town on to commit atrocities against Poles. During the German occupation, Poles were subject to persecutions, mass arrests, expulsions and massacres. Numerous Poles were imprisoned in a concentration camp in Radzim and in a prison established by the "Selbstschutz" in Sępólno Krajeńskie, and later murdered there or deported to other Nazi concentration camps. Mass arrests of Poles were carried out from September 1939. In 1945 the town was restored to Poland.