Fort Union Trading Post National Historic Site Located near Williston, ND TRAVEL BASICS - CAMPING - LODGING ACTIVITIES - FACILITIES - FEES/PERMITS Fort Union's courtyard, with Bourgeois House, tipi, and Red River cart visible. (NPS Photo) IN BRIEF John Jacob Astor's American Fur Company built Fort Union Trading Post in 1828 near the junction of the Missouri and Yellowstone rivers in what is now ...