There are twenty-eight threatened and endangered animals in Illinois that require a forested habitat for some portion of their life cycle. These animals include the Common Barn Owl (Tyto alba), the dusky salamander (Desmognathus fuscus), the bobcat (Lynx rufus), the eastern massasauga snake (Sistrurus catenatus) and one insect, the hoary elfin (Incisalia polios), a small brown spring butterfly that has a white patch on the rear underwing. 

Illinois forests are also a summer breeding ground for many migrating neotropical birds. Forests are home to 61% of the state's native plants, and nearly half of all of the threatened and endangered plants in Illinois grow in forest habitats. Many of the state's wild orchids also require forest habitat.