After Hitler came to power in 1933, many thousands of Jews left for the Netherlands, among other places. On 15 December 1938, the Dutch government closed its border to refugees, but organised a camp in Drenthe in the northeast; it was partly funded by Dutch Jews for Jewish refugees.
Prior to the German occupation, Westerbork housed around 750 people, but after the German government took control of the Netherlands they were detained, had to undertake forced labour, and Westerbork became a deportation camp.
By July 1942 the German security police had full control of Judendurchgangslager Westerbork, the only purpose of which was to deport Jews and gypsies (Sinti and Roma) to the east. The first transport of Jews took place on 15 July, to be followed by 92 others. Most died in Auschwitz-Birkenau or Sobibor. A total of 101,525 Jewish prisoners passed through the transit camp – the vast majority spending only a few weeks there – sometimes only a few hours. More than two hundred Jews escaped from the camp.
See http://en.wikipedia.org/wiki/Westerbork_transit_camp and http://www.kamparchieven.nl/en/camps-in-the-netherlands/camp-westerbork for further information – from which sources these details have been drawn.