Thousands. Antelope Island, in Utah, usually has around 600-800 head. I barely got into the edge of Yellowstone the other day and saw several dozen right off. They manage a hunt around the park when the population gets too big. There are a few people in Tennessee that raise herds. I read a while back that the wild bison population in the US is around 20,000. There are roughly 1/2 a million that are raised privately for commercial purposes. Population estimates of the 1700's are around 30-40 million.