[3] Fall River County lies at South Dakota's SW corner.

Outside the mountainous area, the county's highest point is its SW corner, at 3,970 ft (1,210 m) ASL.

Of the several peaks in the mountainous area, one in the NE portion of that zone rises to 4,646 ft (1,416 m) ASL.

[4] As of the 2020 census, there were 6,973 people, 3,226 households, and 1,891 families residing in the county.

In terms of ancestry, 39.7% were German, 12.6% were Irish, 11.2% were English, 8.4% were Norwegian, 5.9% were Dutch, and 2.3% were American.

In no national election since 1936 has the county selected the Democratic Party presidential candidate.