Pennington County is a county in Western South Dakota that covers 2,784 square miles and borders Wyoming to the west. It is the second most populous county in South Dakota. Large communities include Rapid City, Hill City, Wall, Box Elder, New Underwood, and Keystone.
Pennington County was formed by the Dakota Territorial legislature in 1875, and was named in honor of the territorial governor, John Pennington. The Black Hills were still part of the Great Sioux Nation under the terms of the Laramie Treaty of 1868, when white settlers first occupied the bottomlands along Rapid Creek. The settlement took the name of "Hay Camp".