| Armstrong County, South Dakota | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1883–1952 | |||||||||||||
 Armstrong County (red) and Stanley County (pink) | |||||||||||||
| Area | |||||||||||||
| • Coordinates | 44°45′N 101°00′W / 44.75°N 101.0°W | ||||||||||||
• 1950 | 1,359.744 km2 (525.000 sq mi) | ||||||||||||
| Population | |||||||||||||
• 1950 | 52 | ||||||||||||
| Status | Unorganized county in South Dakota | ||||||||||||
| • Type | Attached to Stanley County with appointed officers | ||||||||||||
| History | |||||||||||||
• Established | March 8, 1883 | ||||||||||||
• Disestablished | 1952 | ||||||||||||
| |||||||||||||
| Today part of | Dewey County | ||||||||||||
Armstrong County was a county in the U.S. state of South Dakota, and its predecessor Dakota Territory, between 1883 and 1952. Located in the western part of the state, it was a sparsely-inhabited part of the Cheyenne River Indian Reservation that relied primarily on the cattle trade and the Missouri and Cheyenne Rivers. Never having an organized county government in its own right, it was attached to Stanley County, with its county seat at Fort Pierre, for administrative purposes.
An unrelated "Armstrong County" had existed in the eastern part of the Dakota Territory between 1873 and 1879. Pyatt County was established in 1883 in the western part of the territory near the Missouri River, and was renamed Armstrong County in 1895. Having lost a significant part of its territory to Stanley and Ziebach Counties between 1898 and 1911, its subsequent population was so low that it set several records: it was often the only county in the nation to cast the entirety of its votes to one presidential candidate, by 1940 it was the only county without a post office, and by 1950 it was the only county without a single employee of the federal government.
The construction of the Oahe Dam flooded out most of the valuable land in the county. Dewey County, which had refused to annex the county in the past, finally did so in 1952. Oddly enough, the site of Armstrong County is now home to several more homesites than it had when it was a county.