The Yellowstone Park bison herd is a bison herd in Yellowstone National Park. It is probably the oldest and largest public bison herd in the United States, estimated in 2020 to be 4,800 bison. The bison in the Yellowstone Park bison herd are American bison of the Plains bison subspecies. Yellowstone National Park may be the only location in the United States where free-ranging bison were never extirpated, since they continued to exist in the wild and were not reintroduced.