Contour maps showing the concentration of selected inorganic ions across the state of Ohio illustrate that high concentrations of some ions visually correlate with the location of major geologic features, whereas other ions are randomly distributed. Strontium and sulfate have high concentrations over the Cincinnati, Findlay, and Kankakee arches, where carbonate aquifers containing gypsum and celestite are located. The highest concentrations of potassium and beryllium are located along the Cambridge fault zone, a major structural feature in eastern Ohio. High concentrations of iron and nitrate are found adjacent to single wells. Nitrate highs may be related to anthropogenic contamination, whereas some iron anomalies are located where sulfate is high. The maps produced in this study indicate that statewide contour maps of ion concentrations are useful for correlating aquifer chemistry with the regional geology of an area and determining the background level of ions on a state-wide scale.