The U.S. Geological Survey collects, on a systematic basis, data needed to determine and evaluate the ground-water resources of Harrison County, Mississippi. Water samples were collected from 1997 to 2005 at selected wells screened in the Citronelle, Graham Ferry, Pascagoula, Hattiesburg, and Catahoula Sandstone aquifers and were analyzed for field properties (temperature, pH, specific conductivity, and color), total dissolved solids, chloride, iron, and manganese. The U.S. Environmental Protection Agency Secondary Drinking Water Regulation (SDWR) of 500 milligrams per liter for total dissolved solids was exceeded in water from three wells in the Hattiesburg aquifer and 12 wells in the Pascagoula aquifer. Chloride concentrations did not exceed the SDWR in any of the aquifers sampled, except for the Pascagoula aquifer where water in 10 wells had concentrations that exceeded the SDWR of 250 milligrams per liter. Iron concentrations in water from nine wells completed in the Graham Ferry and four wells completed in the Pascagoula aquifers exceeded the SDWR of 300 micrograms per liter. Thirty water samples collected from the Graham Ferry and 12 from the Pascagoula aquifer exceeded the SDWR of 50 micrograms per liter for manganese.