Fort Gibson, Cherokee Nation and Fort Washita, Choctaw Nation, were two of the most important Indian Nation forts. Fort Gibson was about 60 miles north and east of Fort Smith, near the present town of Muskogee OK. The Fort area was occupied by the army in 1824 making it the oldest military establishment in Indian Territory. The extant covers from Fort Gibson after July 1, 1851 is small compared to the mail volume previous to this (see the companion page under pre-1851 period).
Fort Washita was a bit over 100 miles straight north of present day Dallas Texas, just over the Texas border in the Indian Nations. The Fort was built in 1842, occupied by Confederate forces at the beginning of the war, and never reoccupied by federal forces after the war.