Shannon County is a county located in the U.S. state of South Dakota. The population was 13,586 at the 2010 census. Its largest community is Pine Ridge.
The county is entirely within the Pine Ridge Indian Reservation and contains part of Badlands National Park. The county's per-capita income makes it the second poorest county in the United States. (Buffalo County, South Dakota, is the poorest.)
In recent years, its residents have become more politically active, voting in state and national elections. A voter registration drive in 2002 helped gain support for the Democratic candidate for the US Senate, and turnout in Shannon County and across the Pine Ridge Indian Reservation helped narrowly elect Tim Johnson to office. The county has the distinction of having the highest percentage of Democratic votes for President in the 2004 election of any county in the US (85%) and in 2008 with 88.69% of votes cast for Barack Obama. It is an alcohol prohibition or dry county; i.e., taxes on alcohol illegally consumed within the county go to other counties .
Shannon County is one of two counties in South Dakota that does not have its own county seat (Todd County is the other). Hot Springs in neighboring Fall River County serves as its administrative center. It is also one of five South Dakota counties that are entirely on an Indian reservation. (The others are Corson, Dewey, Todd, and Ziebach.)
Until 1982 Shannon and Washabaugh County, South Dakota, were the last unorganized counties in the United States. Although it was organized and received a home rule charter that year, Shannon, as noted above, contracts with Fall River County for its Auditor, Treasurer, and Registrar of Deeds.
It has an unusually low Human Development Index of 0.703 (Medium) compared to the national average of 0.950 (Very High).