The Gulf Coast Regional Aquifer-System Analysis is a study of regional aquifers composed of sediments of mostly Cenozoic age that underlie about 230,000 sq mi of the Gulf Coastal Plain. These regional aquifers are part of three aquifer systems: (1) the Mississippi Embayment Aquifer System, (2) the Texas Coastal Uplands Aquifer System, and (3) the Coastal Lowlands Aquifer System. The water chemistry of the Lower Wilcox Aquifer, which is part of the Mississippi Embayment Aquifer System is presented by a series of maps. These maps show the areal distribution of (1) the concentration of dissolved solids and temperature, (2) the primary water types and pH, (3) the concentration of major ions and silica, and (4) the milliequivalent ratios of selected ions. Dissolved constituents, pH, temperature, and ratios are based on the median values of all samples in each 100-sq-mi area. The concentration of dissolved solids in water from the Lower Wilcox Aquifer ranges from 18 mg/L near the outcrop in western Tennessee to 122,000 mg/L in a down-dip area in southern Mississippi. The primary water type is calcium bicarbonate in the outcrop area and sodium bicarbonate in all other areas of the aquifer within the limits of available data. The concentrations of major ions generally increase from the outcrop area to the down-dip limit of the data in the southern part of the aquifer area east of the Mississippi River. The milliequivalent ratio maps of selected ions in water from the Lower Wilcox Aquifer indicate some trends. The milliequivalent ratio of magnesium plus calcium to bicarbonate ranges from less than 0.1 to 40.4 and generally decreases from outcrop to down-dip limit of the data in the southern part of the aquifer area east of the Mississippi River. The milliequivalent ratio of bicarbonate to chloride ranges from 0.01 in southern Mississippi to 52.3 in northwestern Mississippi. This ratio increases from the outcrop toward the Mississippi River and from north to south in the northern part of the aquifer area east of the Mississippi River whereas the ratio increases from outcrop to mid-dip and decreases from mid-dip to down-dip limit of the data in the southern part east of the Mississippi River.