Well and chemical groundwater data contained in three tables were collected during a 5-year study started in 1971 to determine the geology and water resources of Deuel and Hamlin Counties, South Dakota. Physical, hydrologic, and geologic data for 3,228 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 tables in the report are computer printouts from WATSTORE. Water quality data from 564 chemical analyses have been stored in the Water-Quality File of WATSTORE and is computer printed in the chemical analyses table by aquifer. (USGS)