Fox squirrel (Sciurus niger) populations in the southeastern United States are declining, with fragmentation of large mature forests believed to be the primary cause. Historically, demographics of midwestern fox squirrel or gray squirrel (Sciurus carolinensis) populations have been applied to management of southeastern fox squirrels. However, fox squirrels rarely become abundant in southeastern forests, despite variations in habitat quality. Previous research has reported on low density populations in the Southeast, but the effects of changing land use patterns on population demographics remain untested. We studied the demographics of a stable high density population of southern fox squirrels (S. n. niger) on Spring Island, South Carolina. Squirrel density (75.8 squirrels/km²), as estimated by the mark–resight method was the highest reported for fox squirrels in the Southeast. Mean annual survival rate was 62%, with automobiles causing 31% of squirrel deaths. Seasonal weights (992 g–1150 g), age structure (39% juvenile and 61% subadult or adult) and evidence of year round breeding suggest the population was healthy despite concurrent residential development of the island. Although individual home ranges were smaller (2.13 ha for females during late summer to 15.08 ha for males during early summer) than previously reported, we observed no resource related sexual segregation or intolerance among individuals. We believed the characteristics of this unique population were directly related to the sustainable availability of a diversity of fox squirrel foods. These findings suggest that population demographics of fox squirrels might differ greatly among habitats, even within similar geographic locations and the same subspecies. Therefore, managers should recognize that southern fox squirrel populations can thrive in forests with residential development when cover and food resources are abundant and sustainable.