Federally listed species are by definition listed in Illinois, although not all federally listed species occur in Illinois. Additional species not listed at the federal level are listed by the state for protection based on the Illinois Endangered Species Protection Act and criteria outlined by the Illinois Endangered Species Protection Board.
The "Checklist of Illinois Endangered and Threatened Animals and Plants" maintained by the Illinois Endangered Species Protection Board currently lists more than Illinois 350 species as endangered and more than 100 species as threatened in Illinois. The majority of Illinois listed species are plants, but Illinois threatened and endangered species also include fishes, amphibians, reptiles, birds, mammals, mollusks, and arthropods.