During the German invasion of Poland, which started World War II, the Wehrmacht arrived in Brzesko on 5 September 1939. Soon afterwards, the "Einsatzgruppe I" entered the town to commit various atrocities against the populace. Under German occupation, the town became part of the "kreis" (county) Tarnów in the Kraków District of the General Government, a separate administrative region of the Third Reich. 44 people were killed and about 200 were injured as they were waiting for the evacuation trains from Silesia. Several Poles from Brzesko were murdered by the Russians in the large Katyn massacre carried out in April–May 1940. A closed Jewish ghetto existed between spring 1941 and September 1942. It spread across 3 areas: Berka Joselewicza Street, then all the buildings north of the Market Square up to the Rynek Sienny (known today as Sobieskiego Street and Chopina Street), and finally Głowackiego Street up to Trzcianka and the Kazimierza Wielkiego Square. Several Poles were imprisoned by the Germans in the local prison and then deported to concentration camps for rescuing Jews. The Red Army arrived in Brzesko on 19 January 1945, and then the town was restored to Poland.