Fort Gibson is a historic military site located next to the present day city of Fort Gibson, in Muskogee County Oklahoma. It guarded the American frontier in Indian Territory from 1824 until 1888. When constructed, the fort lay farther west than any other military post in the United States; it formed part of the north–south chain of forts intended to maintain peace on the frontier of the American West and to protect the southwestern border of the Louisiana Purchase.