Fort Saint Vrain was an 1837 fur trading post built by the Bent, St. Vrain Company, and located at the confluence of Saint Vrain Creek and the South Platte River, about 20 miles (32 km) east of the Rocky Mountains in the unorganized territory of the United States, in present-day Weld County, Colorado.

William Clark, governor of the territory, granted the Bent, St. Vrain Co. a license to trade on November 8, 1836.

It accommodated trade with Native American tribes and mountain men engaged in fur trapping.

He employed such notable people as James Beckwourth, a mountain man, and Jean Baptiste Charbonneau, who was born to Sacajewea during the 1804-1806 Lewis and Clark Expedition.

She accompanied the expedition with her husband, trader & trapper Toussaint Charbonneau as well as newborn Jean Baptiste, while filling the crucial role of translator to the Shoshone Indian tribe.