Arsenic concentrations were compiled for 173 wells in an agricultural region of west central Texas. Wells in the study area produce water from the High Plains (Ogallala) Aquifer. Historically, arsenic compounds were applied to cotton fields in the study area, and they are also present in local rock formations. A geographic information system (GIS) was used to map and evaluate arsenic levels in groundwater. Arsenic was detected in every well, in concentrations ranging from 1.1–171.9 μg/L. Ten observations exceeded 10 μg/L. Several lines of evidence suggest the arsenic came from pesticides instead of local rock formations. These include higher arsenic levels at shallower water table depths, other agricultural chemicals in groundwater, incompatible hydraulic head differentials between the High Plains Aquifer and potential arsenic‐bearing formations, and low arsenic levels in groundwater of potential arsenic‐bearing formations.