During the war, the SS incarcerated more than 10,000 Soviet prisoners of war at Mauthausen, including 3,000 held at the Mauthausen subcamp Gusen. Nationals of virtually every German-occupied country in World War II came through Mauthausen. These included, among those prisoners who were registered: more than 37,000 non-Jewish Poles, nearly 23,000 Soviet civilians, between 6,200 and 8,650 Yugoslav civilians, approximately 6,300 Italians after September 1943, and at least 4,000 Czechs, and, eventually, in 1944, 47 Allied military personnel (39 Dutchmen, 7 British soldiers and 1 US soldier), all of them agents of the British Secret Operations Executive. Further, the SS transported other thousands of prisoners to Mauthausen to be murdered without ever being registered as prisoners in the camp.
Before May 1944, the SS incarcerated relatively few Jews at Mauthausen. The total number of Jewish prisoners at Mauthausen between 1938 and the end of February 1944 was around 2,760. Most of them were reported dead by the end of 1943. From March through December 1944, at least 13,826 Jews arrived in Mauthausen, most of them Hungarian and Polish Jews and approximately 500 of them women. The SS had deported virtually all of them from Auschwitz-Birkenau and Plaszow camps to Mauthausen. In all, the SS registered 25,271 Jews in the Mauthausen camp complex, though the actual number of Jews, including arrivals during the last week of the war when the prisoner registration process broke down, may have pushed the number as high as 29,500.
Other than four Yugoslav women whom the SS brought to Mauthausen with 46 men to be shot in April 1942, the first female prisoners in Mauthausen were two dozen women from Ravensbrück, whom the SS transferred to provide sex for favored male prisoners. The women arrived in June 1942 and lived in the first bordello established in the Nazi concentration camp system. Over the next two years, the SS brought a few hundred women to Mauthausen either to kill them or to hold them temporarily in transit before transfer to other camps.
The first women registered as prisoners at Mauthausen (as opposed to Ravensbrück, arrived on October 5, 1943. With the arrival of more women in 1944, the Inspectorate of Concentration Camps classified Mauthausen as a women's concentration camp (Frauen-Konzentrationslager) on September 15, 1944. By the end of September 1944, 459 women were in the main camp: 392 political prisoners (non-Jewish), 38 Jehovah's Witnesses, and 29 so-called asocials. Six months later, on March 31, 1945, the SS reported 2,252 female prisoners in the Mauthausen system. Again, the majority were non-Jewish political prisoners (1,453), but the 608 Jewish women belonged to the second largest female prisoner category. Also reported among the female prisoners were 43 Jehovah's Witnesses, 79 Gypsies (Roma), 62 so-called asocials, 5 women classified as Spanish Republicans, and 2 as convicted criminals. By February 1945, the SS had set aside three barracks in the main camp for female prisoners.
The main Mauthausen camp (Stammlager) had three principal sections: Camp I, the original protective detention camp; Camp II, the camp workshop area, where prisoners were forced to work, and which the SS later converted to prisoner barracks in spring 1944; and Camp III, built in the spring and summer of 1944 to accommodate the influx of Hungarian Jews. Located at the opposite side of the roll call square from Camp I was a chain of long stone buildings that housed various camp services such as the prisoners' kitchen, showers, laundry, the bunker and, eventually, the gas chamber. Nearby stood the crematoria facilities along with the site where the camp staff shot prisoners.
To the west, off the entrance road to the main camp, was the so-called infirmary camp. The SS originally constructed this facility in fall 1941 for Soviet prisoners of war; hence it was frequently referred to as the "Russian camp." From the spring of 1943, the camp authorities incarcerated ill or weak prisoners in this "infirmary" camp, where patients received little or no treatment and most eventually died. East northeast of the main camp was the so-called tent camp, which consisted of 14 large tents with a total inner surface of 6,200 square yards. The camp authorities erected it in the autumn of 1944 to accommodate large groups of prisoners evacuated from concentration camps and forced-labor camps in the East. In the winter of 1945, the overwhelming majority of inmates in the so-called tent camp were Hungarian and Polish Jews.
The various camps were surrounded by walls and/or electrified wire. Watchtowers and SS guards surrounded the entire complex. The SS commandant's office and the barracks for the SS administrative personnel and guard units were located west of the camp.
In January 1941, SS General Reinhard Heydrich, the chief of the Reich Main Office for Security (Reichssicherheitshauptamt; RSHA), designated Mauthausen as a category III concentration camp, in which the SS would incarcerate only those prisoners whom the RSHA deemed to be "severely incriminated, especially previously convicted criminals and asocials—that means protective detainees who have only remote potential for reform."
An estimated 197,464 prisoners passed through the Mauthausen camp system between August 1938 and May 1945. At least 95,000 died there. More than 14,000 were Jewish.