On December 8, 1941, the killing center at Chelmno (Kulmhof) was opened in the Wartheland district of Poland. Chelmno was located on the grounds of an unused manor house. The first victims of Chelmno were mainly residents of nearby towns and villages in the Wartheland district. In January 1942, many residents of the Lodz ghetto were deported to the camp. When the Wartheland became almost completely judenrein (free of Jews) in March of 1943, excepting the remaining inhabitants of the Lodz ghetto, Chelmno was closed. It reopened in June 1944 to receive Jews from the liquidation of the Lodz ghetto. The Germans abandoned the Chelmno Killing Center on January 17, 1945. Between December 1941 and March 1943 and in June/July 1944, the SS killed at least 172,000 people at Chelmno.

Chelmno was the first stationary facility to use poison gas to kill its victims. When victims arrived at Chelmno, they were told by SS dressed in white lab coats that they were going to be taken to Germany as laborers. The SS then led prisoners into large vans, which would be filled with 50-70 people. They sealed the doors of the van and connected the exhaust pipe to the body of the van. When the prisoners had asphyxiated on the carbon monoxide, their bodies were dumped in mass graves in the forest.

Gas vans had previously been used at Chelmno in the T4, or “euthanasia,” program. They had also been tested on Soviet prisoners of war at Sachsenhausen. The use of gas began to replace, though never completely, the killing of victims by shooting. Putting the victims in vans and eventually gas chambers allowed the Nazis to depersonalize the murders. Death in these situations did not seem to the Nazis as though it was at the hands of their men, but rather remote and secret.

The opening of Chelmno serves as an important marker in the thought of the SS. In the month preceding the opening of Chelmno, the SS began to construct the gas chambers at Belzec. With the use of gas in the killings, the mechanization and evolution of the Holocaust grew.