[2] The county was named for Dighton Corson, a native of Maine, who came to the Black Hills in 1876, and in 1877 began practicing law at Deadwood.

The county is encompassed within the Standing Rock Indian Reservation, which extends into North Dakota.

Corson County lies on the north line of South Dakota.

The Missouri River flows south-southeastward along its eastern boundary line.

[3] The Grand River flows eastward through the central part of the county to discharge into the river, and Standing Cloud Creek flows eastward through the county's lower SW area.

The terrain generally slopes to the east and south; its highest point is near its NW corner, at 2,582 ft (787 m) ASL.

[6] [3] As of the 2020 census, there were 3,902 people, 1,196 households, and 825 families residing in the county.