During the joint German-Soviet invasion of Poland, which started World War II, in September 1939, Janów was three times bombed by the Luftwaffe, which killed 350 people and destroyed 85% of the town. The town was afterwards occupied by Germany. At least 17 Poles from the county were murdered by the Russians in the large Katyn massacre in April–May 1940, while in June 1940, the Germans carried out mass arrests of local Poles during the "AB-Aktion". Arrested Poles were imprisoned in Lublin, and then often deported to the Sachsenhausen and Auschwitz concentration camps, while some were murdered during large massacres of Poles committed in Rury, Lublin. A forced labour camp was opened in 1940, and town’s Jewish population was persecuted by the occupiers. There were several Jewish partisan groups operating in the Janów forests for the duration of the war. Despite this, only around 20 Jews from the town survived the Holocaust out of 3,500 to 5,000 Jews who lived in the town before the war.