 Settlement in the area began in 1805 when the US military bought a nine @-@ square @-@ mile tract of land at the confluence of the Mississippi and Minnesota River from the Sioux Nation . On a bluff overlooking the rivers , Fort Snelling , a military outpost , was built under the command of Colonel Josiah Snelling between 1820 and 1824 . In 1821 Snelling 's son , William Joseph Snelling came to the fort after leaving West Point and spending a year with friendly Sioux . According to a Minnesota history account written in 1858 , " The year after he came to the fort young Snelling set out in company with Joseph R. Brown , a frontiersman and local celebrity , to explore the rivulet that supplies the cascade of Minne Ha @-@ Ha , as far as Lake Minne Tonka . " Both " men " were 17 @-@ year @-@ old boys at the time . 
