[3] The Upper Sioux Indian Reservation, related to the historical Yellow Medicine Agency that was here, is entirely within the county.

It was established under the Treaty of Traverse des Sioux in 1851, by which the Dakota ceded much territory in the region to the United States.

Its name comes from Yellow Medicine River, which runs through the eastern part of the county to the Minnesota.

The river's name derives from the moonseed plant, Menispermum canadense, whose yellow root the native Dakota people used for medicinal purposes.

The state legislature approved the petition (subject to local voter approval), and Governor Pillsbury signed the act on February 27, 1879, but the proposal failed to garner a combined majority of votes in the three counties, and the proposed Canby County[5] did not come into being.

The Stony Run Creek flows east through the northeast part of the county; the Florida Creek flows northeast through the west end of the county, and the Lac qui Parle River also flows northeast through the west central part of the county.

[7] The terrain slopes to the east and slightly to the north; its highest point is on the west border, near its SW corner, at 1,732 ft (528 m) ASL.

The county gave a majority to Barack Obama in 2008, but has trended more Republican in recent cycles.