The source is IDOT's ArcGIS server: http://ags10s1.dot.illinois.gov/ArcGIS/rest/services/SafetyPortal/SafetyPortal/MapServer/12 It was obtained using pyesridump, created by Ian Dees.
IDOT asks that this disclaimer appears anywhere the data is used: "The motor vehicle crash data referenced herein was provided by the Illinois Department of Transportation. The author is responsible for any data analyses and conclusions drawn."