Well and chemical groundwater data contained in two tables were collected during a 5-year study started in 1967 to determine the geology and water resources of Brown County, South Dakota. Physical, hydrologic, and geologic data for 3,127 wells and test holes have been entered into computer storage in the Ground-Water Site Inventory File of the U.S. Geological Survey 's National Water Data Storage and Retrieval System (WATSTORE). The well table in the report is a computer printout from WATSTORE. Water quality data from 750 chemical analyses has been stored in the Water-Quality File of WATSTORE and is computer printed in the chemical analyses table by aquifer. (USGS)