In September 1939, Serock was a place of fighting between the Poles and the invading Germans during the Invasion of Poland, which started World War II. On September 5, 1939, around 50-70 people, both inhabitants of Serock and refugees from nearby Nasielsk, were killed in a German air raid. In mid-September 1939, the "Einsatzgruppe V" entered the town to commit atrocities against the population.