A 'camptown' was a temporary workingmen's tent or shack settlement. According to Wikipedia, Foster's 'camptown' was in Pennsylvania.
Camptowns grew and were dismantled as the railroads moves west, and with other longer term construction projects.

"The rag-tag mix of horses that are racing, and the disorder of the racing conditions at the ramshackle camptown track, provide the fun, with the usual unspoken undercurrent of superiority among the entertained hearers." Wikipedia.