The Chicago metropolitan area includes Chicago, Illinois, and suburban areas, which are closely linked to the city through geographic, economic, and cultural ties. The Region to be mapped for the Chicago mycobiota covers nine counties in northeast Illinois (Cook, DeKalb, DuPage, Kane, Kankakee, Kendall, Lake, McHenry, Will) and three counties in northwest Indiana (Lake, LaPorte, Porter). This area totals 22,592 km2, with a 2013 population of 9.5 million inhabitants.
Cook County is the largest county (4,235 km2), with 2013 population of 5.2 million, and contains the city of Chicago. Cook County features an extensive system of forest preserves (started in 1914 and covering 11% of county land area) and is the best-documented county in the region in terms of its mycobiota, with 800 species of macrofungi recorded.
The second most documented is Porter County, Indiana, which contains the major portion of Indiana Dunes National Lakeshore, plus Indiana Dunes State Park.
This twelve-county region has eight State Parks and several State Nature Preserves, but no State Forests. Federal lands include Indiana Dunes National Lakeshore and Midewin National Tallgrass Prairie.