River, southwestern Minnesota into Iowa, U.S. Rising near Pipestone , it flows 525 mi (845 km) southeast to join the Mississippi River near Keokuk, Iowa.
Above Humboldt, Iowa, it is known as the West Fork. From the late 1830s until the end of the American Civil War , it was the main commercial artery for central Iowa. It was early utilized for power, and, although none survive, 80 grain mills were built (184090) along its banks.