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.
These documents have been digitized and are listed alphabetically by the watershed/region name. The shaded area in the small maps click to enlarge images) indicate the geographic coverage of the corresponding documents.