Abstract Eversgerd Post Oak Flatwoods is a 16 ha woodlot that is part of an extensive band of timber associated with the broad Kaskaskia River valley in the Southern Till Plain Natural Division of Illinois. This flatwoods was studied to determine its woody composition and structure, and the effects of fire suppression on canopy closure and plant succession. Tree density within the site averaged 266 trees/ha with a basal area of 24.8 m2/ha. Quercus stellata Wang. (post oak) dominated the overstory and woody understory with an importance value of 171 (200 possible). Quercus bicolor Willd. (swamp white oak) and Q. palustris Muenchh. (pin oak) were common species in a shallow depression, accounting for their second and third in importance value ranking. The forest has an open, park-like appearance. Small woody saplings averaged 820 stems/ha and large saplings averaged 221 stems/ha. Grasses and sedges dominated the herbaceous layer; Danthonia spicata (L.) Roem. & Schultes and Carex cephalophora Willd. were the dominant species. The large number of post oaks with low branches and branch scars indicate that this forest was more open in the past.