Flying squirrels (genus Glaucomys) have a close association with forest trees for food, shelter, and travel. They play a key role in dispersing seeds and fungi, as well as being an important food source for predators. Thus, understanding their habitat requirements provides insight for conservation efforts, particularly in highly fragmented areas. This study employed radio-telemetry to examine habitat use by Glaucomys volans (Southern Flying Squirrel) in urban and rural fragments in southwestern Illinois. While male home-range sizes were not observed to be significantly different from females, squirrels exhibited significant preference for medium and large trees (>40 cm diameter) over small trees (≤40 cm diameter). Additionally, squirrels selected soft-mast trees for nesting significantly more than expected, with no relationship found between the proportion of hard-mast trees used and home-range size.