Here we have listed some of the more important resource links as well as additional contacts for GIS information.
What is GIS? ESRI
Chicago Metropolitan Agency for Planning (CMAP)
Regional Transportation Authority
United States Geological Survey
United States Census Bureau
FEMA (Flood Maps)
National Geodetic Survey (Survey Benchmark Data)
Cook County, IL
DeKalb County, IL
DuPage County, IL
Grundy County, IL
Kane County, IL
Kankakee County, IL
Kendall County, IL
Lake County, IN
Lake County, IL
McHenry County, IL
ESRI
ILGISA
URISA
IPLSA