Located in southeast Wisconsin, Jefferson County is almost entirely blanketed by sediments that were delivered or shaped by the ice sheet that covered this area during the last ice age. New mapping interprets the distribution of the bedrock surface that is buried beneath those glacial sediments as interpreted by three drill cores, over 13,000 well construction reports, examination of well cuttings, and 34 geochemical profiles of boreholes. This mapping will support parallel efforts to characterize how the bedrock affects groundwater quality. Includes map, 5-page report, geochemical data, raster of bedrock elevation surface, and GIS data in the geologic map schema (GeMS) format.