Allerton Park has long been recognized as one of Illinois’ most significant natural areas. It is located in the Grand Prairie Natural Division and contains outstanding examples of old-growth floodplain and upland forest. Allerton Park is one of only three areas in central Illinois with over 500 acres of contiguous forest. The high diversity of natural communities and native species, especially forest trees and wildflowers, and the park’s location along an unmodified reach of the Sangamon River also contribute to the high natural quality of the site. A portion of the site has been recognized as a National Natural Landmark by the U. S. Park Service.