Saltwater intrusion into coastal aquifers poses a threat to drinking water sources. We evaluate the plausibility of saline-water intrusion into the Surficial Aquifer of a barrier island on Georgia’s coastal plain. Using a transect of shallow wells, we monitored groundwater levels, specific conductivity, chloride concentration, and the d²H and d¹⁸O within groundwater. We sampled precipitation and water in an adjacent tidal creek to evaluate the mixing of components. We test a conceptual model that predicts enhanced saline water intrusion along island margins and lesser saline water intrusion toward the island interior. This conceptual model was not completely verified. Instead, specific conductivity and chloride concentrations in groundwater were greatest at an inland location, not at the island margin. Overall, the isotope composition of all groundwater samples paired with hydrometric and tidal data seems to suggest marginal water delivery from the coastal rivers into the terrestrial aquifer, except in areas proximal to a relic drainage ditch that apparently serves as a preferential flow pathway for highly saline water into the island interior.