There seems to be some stark contrasts in South Dakota.
South Dakota has the "low" spots of Corson, Dewey, and Zieback counties in the central north which corresponds to Standing Rock (crossing the ND border as Siouxland county) and Cheyenne River. Not much in the way of resources and a long history of poor infrastructure.
Buffalo County is the Crow Creek Indian Reservation. You can see the difference between Crow Creek and Lower Brule Reservation (amazing what a difference the other side of the river is and being an exit away from I90).
Shannon and Todd county are Pine Ridge and Rosebud reservations. These are probably the two poorest reservations in the area. The alcohol problem has been the overriding factor as well and not developing any businesses of note.
Bennett and Jackson are mostly National Parks and National Wildlife Refuges.
South Dakota also took a hit on the early storm last year that killed tens of thousands of cattle (early storm, started with rain, freezing winds, cattle didn't have winter coats, and were still in the summer pastures).
Further up in Westchester and Rockland you find areas that are really deep in poverty but don't have easy access to reliable public transportation to places where jobs are more easily found.