13 Polish soldiers were killed on September 2, 1939, during the German invasion of Poland, which started World War II. In mid-September 1939, the German "Einsatzgruppe IV" entered the town to commit atrocities against the population. During the German occupation, the Polish population was subject to mass arrests, expulsions and massacres. The Germans established a prison for Poles, in which 606 people died. Many Polish inhabitants of Koronowo and nearby villages were murdered by the Germans in nearby Buszkowo on 5–6 October 1939 and in the forest near Koronowo on 26 October 1939. Among the victims were local merchants, craftsmen and pre-war mayor Maksymilian Talaśka. The Germans burned the bodies of the victims in attempt to cover up the crime. Koronowo was captured by the Soviets in January 1945 and restored to Poland.