Athearnia anthonyi (Redfield, 1854) is a federally endangered gastropod endemic to the Tennessee River drainage in Alabama and Tennessee. It occurs in only three small populations, the most robust in Limestone Creek, Limestone County, Alabama. In 1996, this population was restricted to the lower 14.5 km of unimpounded stream, confined to riffle and run habitats. A follow-up survey in 2006 suggested no change in range within Limestone Creek. In 1996–97, quantitative data were collected from 4 selected sites in the reach and mean A. anthonyi density was 83.9 ± 9.9 SE per m² (N = 90). Although density did not vary among months, the proportion of individuals within four size classes differed. New recruits appeared in the population between May and July, and a significant die-off of older individuals occurred during the same period. Many individuals were suspected of having at least two breeding seasons. Increasing urbanization within the Limestone Creek watershed necessitates monitoring of A. anthonyi.