Also see the GIS (Geographic Information System) research guide
Illinois Natural Resources Geospatial Data Clearinghouse
Access Illinois GIS data sets and documentation (metadata) for ArcIMS Interactive Map Services, USGS digital topographic maps, aerial photography, orthoimagery, orthophotography, geology, land use, natural resources, and infrastructure.
Coles County GIS
From the Coles County Regional Planning & Development Commission.
U.S. Census Bureau
TIGER/Line Shapefiles Data
Cartographic boundary files for states, counties, and smaller census enumeration units, with additional base data including roads and streams. To access the data, select a year, then click Download and choose "Web interface."
TIGER/Line Shapefiles pre-joined with Demographic Data
A limited set of TIGER/Line Shapefiles are available pre-joined with data in geodatabase and shapefile format.
Historical Census Data (National Historical Geographic Information System - NHGIS)
Summary statistics and GIS boundary files for U.S. censuses and other nationwide surveys from 1790 through the present.
Federal Highway Administration
GIS Data
Highways and bridges. Also contains links to many other federal GIS data sources.
U.S. Geological Survey
National Map Small-Scale Collection
Commonly used base data for the United States.
Other
Geoplatform Data
Searches a comprehensive catalog of government data maintained by Data.gov and only returns geospatial data. GeoPlatform was developed by the member agencies of the Federal Geographic Data Committee (FGDC) through collaboration with partners and stakeholders.
Data.gov
The U.S. Government's open data at the federal, state, and local levels.