A new record low temperature for the entire state of Illinois has now been confirmed. The low of 38 below zero was recorded on January 31, 2019. A committee of people from different agencies in the Midwest reviewed the observation and data around it. The location of the instrument is located in northwest Illinois. Picture of the weather station and location is below (from the NWS Quad Cities).
The previous record was -36° F in Congerville on Jan. 5, 1999.
The all-time record low temperature for Iowa is -47° F. It was set in Washta on Jan. 12, 1912. On Feb. 3, 1996 it was tied in Elkader.
The map below shows the all-time record low temperatures at each reporting station in Illinois. The dots are color coded to what month the record was set.
This link is from the Illinois State Climatologist: https://stateclimatologist.web.illinois.edu/2019/03/06/il/