Following the invasion of Poland at the beginning of the Second World War, Ciechocinek was occupied by Nazi Germany on 12 September 1939 and on 26 September incorporated into the Reichsgau Wartheland as part of the district/county ("kreis") of Hermannsbad (1941-1945). The Polish population was subjected to various crimes including mass arrests, murder and expulsions. During the German invasion, in September 1939, the "Wehrmacht" and "Selbstschutz" murdered some inhabitans of Ciechocinek in the nearby village of Koneck, and from October 1939 to January 1940, the Germans carried out massacres of many Poles from Ciechocinek in the nearby Odolion forest (see "Nazi crimes against the Polish nation"). In addition, in 1939 and 1940, Germans expelled approximately 640 Poles, especially the intelligentsia and owners of shops, workshops and offices, which were then handed over to German colonists as part of the "Lebensraum" policy. During the occupation the town functioned as a military hospital for German troops and also as a health resort, only for German citizens. The town was liberated from occupation in January 1945. Luckily it avoided significant damage.