During the 1990s and early 2000s, agencies including the Illinois State scientific surveys (now in the Prairie Research Institute) collaborated on produce comprehensive assessments on major watersheds and ecological regions of Illinois. The results were published in multi-volume sets known as the "Area Assessments," which cover geology, water resources, biota, human impacts, and (in some cases) pre-settlement/early settlement accounts.
In addition to the technical Area Assessments, summaries written for a lay audience were published for most watersheds/regions, with the title "... An Inventory of the Region's Resources."
Documents are listed alphabetically by the watershed/region name. The shaded area in the maps (taken from the report covers) indicate the geographic coverage of each report.