The National Weather Service (NWS) collects daily temperature and precipitation data for airports in major cities across Illinois. This information is available on their web sites under "local climate". Unfortunately, it is scattered across a number of NWS office web sites. Here I have attempted to consolidate the direct links to that data. The default view is the current month but it includes links to previous versions (aka months) of the table. An explanation of the Weather Service form is found here.
These and other products can be found at the NWS office web sites, as found on weather.gov. On the left hand navigation, under "Climate", select "Local". From there you can select tabs like "observered weather" or "NOWData".