[3] It is named for David S. Stanley, a commander at Fort Sully from 1866 to 1874, which was located nearby.

[4] Stanley County is included in the Pierre, SD Micropolitan Statistical Area.

Stanley County's northwestern boundary is defined by the Cheyenne River which flows eastward, to discharge into the Missouri River at the most northerly point of Stanley County.

The county terrain consists of semi-arid rolling hills, carved by drainages.

[5] The terrain slopes to the east; its highest point is in the SW county corner, at 2,198 ft (670 m) ASL.

In terms of ancestry, 46.4% were German, 12.5% were Irish, 10.8% were English, 10.7% were Norwegian, 8.4% were Czech, 5.0% were Swedish, and 2.5% were American.

The Triple U Buffalo Ranch in northern Stanley County was used in filming the 1990 movie Dances with Wolves.