The Tokio Formation in southwestern Arkansas, hereafter referred to as the Tokio aquifer, is a source of groundwater for agricultural, domestic, industrial, and public use in Clark, Hempstead, Little River, Miller, Pike, and Nevada counties. Water-level altitudes measured 42 wells completed in the Tokio aquifer during 2014 and 2015 were used to create a potentiometric-surface map. In southwestern Arkansas, potentiometric surfaces indicate that groundwater flow in the Tokio aquifer is towards the city of Hope. Northwest of the city of Hope, a cone of depression may exist. In southwestern Pike, northwestern Nevada, and northeastern Hempstead Counties, an area of artesian flow (water levels are at or above land surface) exists.