Johnson County had an estimated population of 24,193 in 1999. Some 5,501 households (approximately 59%) were served by public water. The remainder relied primarily on wells. The estimated population in 2008 was 24,233 with 91 percent served by a water utility.
The Water Resource Development Commission has prepared a report on water supply infrastructure in the county.
It is estimated that there are over 200,000 water wells in Kentucky. The Kentucky Groundwater Data Repository, maintained by the Kentucky Geological Survey, has information on over 50,000 of these wells. The locations of wells and springs in the county for which data are available is shown on the map of wells and springs in Johnson County. A map of certified well drillers in Kentucky has been prepared by the Kentucky Division of Water.