Naturally occurring Sr was found in both surface and ground waters during an investigation of the water resources of Champaign County, Ohio. The Sr is related to the presence of celestite (strontium sulfate) in rocks associated with evaporite deposition. The principal source of celestite in Ohio is in rocks of Late Silurian age. Celestite is present also in the glacial deposits of western Ohio, which contain rock material of Late Silurian age. Total time in contact with the rock material seems to have a large effect upon concentrations of Sr in ground water. Streamflow, during low-flow periods, is made up largely of ground-water seepage and contains detectable Sr. Sr has been found in ground water in other counties in western Ohio and in the brines of eastern Ohio.