As of fall of 2016, Yellowstone National Park estimates that the wild bison population numbers approximately 5,000. This population is comprised of at least two distinct subpopulations, the northern and central herds.
This is a dangerously small number when compared to the tens of millions that used to roam wild across North America. It's frequently and mistakenly argued that 3,000 is too many buffalo, that the number exceeds the ecological carrying capacity of Yellowstone's habitat, thereby justifying the on-going buffalo slaughter under the Interagency Bison Management Plan. A recent study using scientific modeling suggests buffalo "have not reached a theoretical food-limited carrying capacity of 6,200 in Yellowstone National Park."
For detailed bison estimates see our page, Yellowstone National Park Bison Estimates