This has not been an easy question to research as the chaos at the end of the war was not conducive to exact record-keeping. The main sources for the figures I will present below are:
Gutman, Israel, Eberhard Jäckel, and Peter Longerich. Enzyklopädie des Holocaust: die Verfolgung und Ermordung der europäischen Juden. Argon, 1993.
Megargee, Geoffrey P., ed. The United States Holocaust Memorial Museum Encyclopedia of Camps and Ghettos, 1933-1945. Indiana University Press, 2009.
I have also consulted the websites of the various camps' museums and memorials.
Let's take a step back first. What is a concentration camp? For the purposes of this question I am going to assume that you are talking about camps established and run by the Germans. There were concentration camps in other Axis countries (such as Slovakia, Romania, Croatia, Bulgaria), but that would lead us too far altogether. Among the German-run camps, we have to distinguish between the following:
Extermination camps
The extermination camps' only purpose was to kill the people brought there (mainly Jews). Extermination camps were: Treblinka, Sobibor, Belzec, Majdanek, Chelmno and Birkenau (part of Auschwitz).The best known camp, Auschwitz-Birkenau, was actually both a concentration camp and an extermination camp, as was Majdanek. Here's a map. Treblinka, Sobibor, Chelmno and Belzec were dismantled during the war and all the remaining inmates were killed. Majdanek was evacuated before the Soviets overran Lublin and found the camp. Auschwitz was evacuated too, but 7,650 sick prisoners were left behind and liberated by the Soviets.
Jewish Ghettos
These were established mainly in Poland, which had the largest population of Jews of any of the occupied countries, as well as being occupied before the establishment of the death camps. There were also quite a number in the occupied parts of the Soviet Union, as well as a few ghettos in the Baltic states, Rumania, Hungary, Croatia, and lastly the famous Theresienstadt in Czechoslovakia, which was a special case that I have written about here. The purpose of the ghettos was two-fold: imprison all Jewish citizens of a particular area, and extract as much labour from them as possible. As the war went on, all ghettos were gradually “liquidated” (except for Theresienstadt), which meant that the inhabitants were all killed off, either by shootings as in the Soviet Union and Baltic states, or by transportation to a death camp. Theresienstadt held 19,000 prisoners when it was liberated by the Soviets.
Concentration camps
At first, the early concentration camps were established to punish and terrorise the regime's political opponents. From 1936 onwards all concentration camps came under the control of the SS. They expanded the inmate population to include not only political prisoners but also criminals and other “asocial” elements (including Roma and homosexuals). They also started using the camps as a source of productive forced labour. The number of inmates increased dramatically after the onset of war as opponents of the Germans from the occupied countries began flooding in.
As the war neared its end, the Germans started evacuating the camps in the occupied countries and moving all inmates to camps within Germany, often by means of the infamous “death marches”. Many inmates died or were killed on the way, many more died as a result of the appalling overcrowding and lack of food that resulted from this concentrating of prisoners in a very few camps.
We will leave the scattered numbers of very small labour camps out of the picture and concentrate on the main collection camps that were left to be liberated by the Allies in 1945. Here are the numbers:
| Camp | Number of inmates at liberation | Notes |
|---|---|---|
| Bergen-Belsen | 60,000 | |
| Buchenwald | 21,000 | this includes the Ohrdruf subcamp, the first camp liberated by the US~~, made famous by Band of Brothers~~ |
| Dachau | 60,000 | including subcamps, one of which was made famous by Band of Brothers |
| Flossenburg | 1,500 | |
| Gross-rosen | 15,000 | including subcamps |
| Mauthausen-Gusen | 80,000 | including subcamps |
| Mittelbau-Dora | 1,500 | |
| Neuengamme subcamps system | 13,300 | |
| Ravensbrück | 3,500 | including subcamps |
| Sachsenhausen | 3,000 | |
| Total | 258,800 |
Adding Auschwitz and Theresienstadt, we arrive at approximately 285,450 liberated prisoners. A number of these people continued succumbing to disease and malnutrition, and in some cases to re-feeding syndrome, even after liberation, in Bergen-Belsen alone 28,000 did.
