Chełmno extermination camp (German: Vernichtungslager Kulmhof), built during World War II, was the first of the Nazi German extermination camps and was situated 50 kilometres (31 miles) north of the metropolitan city of Łódź (renamed to Litzmannstadt), near the village of Chełmno nad Nerem (Kulmhof an der Nehr in German). Following the invasion of Poland in 1939 Germany annexed the area into the new territory of Reichsgau Wartheland, aiming at its complete "Germanization"; the camp was set up specifically to carry out ethnic cleansing through mass killings. It operated from December 8, 1941 parallel to Operation Reinhard during the most deadly phase of the Holocaust, and again from June 23, 1944 to January 18, 1945 during the Soviet counter-offensive. Polish Jews of the Łódź Ghetto and the local inhabitants of Reichsgau Wartheland (Warthegau) were exterminated there. In 1943 modifications were made to the camp's killing methods because the reception building was already dismantled.

At a very minimum 152,000 people (Bohn) were killed in the camp, which would make it the fifth most deadly extermination camp, after Sobibór, Bełżec, Treblinka, and Auschwitz. However, the West German prosecution, citing Nazi figures during the Chełmno trials of 1962–65, laid charges for at least 180,000 victims. The Polish official estimates, in the early postwar period, have suggested much higher numbers, up to a total of 340,000 men, women, and children. The Kulmhof Museum of Martyrdom  gives the figure of around 200,000, the vast majority of whom were Jews of west-central Poland, along with Romani from the region, as well as foreign Jews from Hungary, Bohemia, Moravia, Germany, Luxemburg, and Austria transported to Chełmno via the Łódź Ghetto, on top of the Soviet prisoners of war. The victims were killed with the use of gas vans. Chełmno was a place of early experimentation in the development of Nazi extermination programme, continued in subsequent phases of the Holocaust throughout occupied Poland.

Russian troops captured the town of Chełmno on January 17, 1945. By then, the Nazis had already destroyed evidence of the camp's existence leaving no prisoners behind. One of the camp survivors who was fifteen years old at the time testified that only three Jewish males had escaped successfully from Chełmno. The Holocaust Encyclopedia counted seven Jews who escaped during the early 1940s; among them, the author of the Grojanowski Report written under an assumed name by Szlama Ber Winer, prisoner from the Jewish Sonderkommando who escaped only to perish at Bełżec during the liquidation of yet another Jewish ghetto in German-occupied Poland. In June 1945 two survivors testified at the trial of camp personnel in Łódź. The three best-known survivors testified about Chełmno at the 1961 trial of Adolf Eichmann in Jerusalem. Two survivors testified also at the camp personnel trials conducted in 1962–65 by West Germany.

www.muzeum.com.pl/en/chelmno.htm