From March through June 1993, the U.S. Geological Survey analyzed water from 150 wells in Jackson County, southeastern Mississippi. The wells are completed in four major geologic units: the Citronelle, Graham Ferry, and Pascagoula Formations and undifferentiated deposits of Miocene age. The wells ranged from 70 to 1,400 feet in depth. Water temperature ranged from 19.0 to 29.5 degrees Celsius; specific conductance (lab), from 32 to 2,340 microsiemens per centimeter; pH (lab), from 5.6 to 9.5; color, from less than 5 to 140 platinum-cobalt units; dissolved-solids concentrations (residue on evaporation), from 22 to 1,260 milligrams per liter; chloride concentrations, from 3.1 to 560 milligrams per liter; and nitrite plus nitrate as nitrogen concentrations, from less than 0.02 to 0.25 milligram per liter. Most of the larger values of specific conductance, color, dissolved-solids concentrations, and chloride concentrations were from wells in the southern one-half of the county. SUMMARY From March through June 1993, the U.S. Geological Survey analyzed water from 150 wells in Jackson County, southeastern Mississippi. The wells are completed in four major geologic units: the Citronelle, Graham Ferry, and Pascagoula Formations and undifferentiated deposits of Miocene age. The wells ranged from 70 to 1,400 feet in depth. Water temperature ranged from 19.0 to 29.5 °C. Specific conductance (lab) ranged from 32 to 2,340 microsiemens per centimeter at 25 °C. The pH (lab) ranged from 5.6 to 9.5. Color ranged from less than 5 to 140 platinum-cobalt units. Dissolved-solids concentrations (residue on evaporation) ranged from 22 to 1,260 milligrams per liter. Chloride concentrations ranged from 3.1 to 560 milligrams per liter. Nitrite plus nitrate as nitrogen concentrations ranged from less than 0.02 to 0.25 milligram per liter. Most of the larger values of specific conductance, color, dissolved-solids concentrations, and chloride concentrations were from wells in the southern one-half of the county. Specific conductance, dissolved-solids concentrations, and chloride concentrations generally increased with depth; however, the relations were poorly defined and showed considerable variation.