Monthly Data By StationMonthly summaries of precipitation, temperature (high, low, mean), heating and cooling degree days, and more from 117 stations throughout the state. Coverage is 1901 to date; date range varies by station.
Current Climate Conditions for IllinoisMaps summarizing precipitation or temperature for the last 7, 30, or 90 days, current month to date, or current year to date.
30 year average high, low, average temperatures and precipitation, calculated from NOAA data, based on 1981-2010. Illinois climate normals based on 1971-2000 can be found in the Internet Archive
Water and Atmospheric Monitoring Program (Illinois State Water Survey)
Illinois Climate Network - Data By StationLatest temperature, precipitation, and wind speed and direction conditions from 19 Illinois Stations. For individual stations, you can download daily data from ~1989 - date (coverage varies by station).
Shallow Groundwater Wells NetworkDepth to water for 35 stations in Illinois ~1950s to date, date range and reporting frequency varies by station.
Midwest Regional Climate Center (Purdue University)
cli-MATE online data portalHourly and Daily data are available for download. Data from stations throughout the U.S. are available, with coverage from the 1800s to date. Years of coverage varies by station. Free registration is required.
Midwest Climate WatchDaily, 7-day, 30-day, and month-to-date maps of temperature, precipitation, snowfall, snow depth, and growing degree days, as well as maps for prior months and seasons.
Fort Armstrong Weather Records 1820-1836Earliest known weather records for Illinois. Scanned from originals owned by the Rock Island Arsenal museum, and posted online by the Illinois State Climatologist