Fort Union Trading Post National Historic Site, reached via US 2 and SR 1804, is 25 miles southwest of Williston, N.D., and 24 miles northeast of Sidney, Mont. Founded by John Jacob Astor for his American Fur Co. in 1828, the trading post became the center for the fur trade on the Upper Missouri River. The fort was 1,800 miles by river from St. Louis, the nearest supply point. Learn More...