 The Midewin National Tallgrass Prairie is a U.S. Forest Service park in the county on the grounds of the former Joliet Arsenal.Other parks include Channahon State Park and the Des Plaines Fish and Wildlife Area.In recent years, average temperatures in the county seat of Joliet have ranged from a low of in January to a high of in July, although a record low of was recorded in January 1985 and a record high of was recorded in June 1988.