Rapid Valley is a census-designated place and unincorporated community in Pennington County, South Dakota, United States, and a suburb of Rapid City. The population was 8,098 at the 2020 census. Rapid Valley has been a retreat for people living in Rapid City due to its low crime, cheap land, and views of the Black Hills. Rapid Valley is home to many industrial and financial businesses, and is the headquarters for many corporations specializing in transport and engineering.