Based on preliminary numbers, the statewide average temperature for May was 61.9 degrees, 0.8 degrees below normal. A few stations in Illinois had highs reaching 90 degrees, including Moline and Springfield. In mid-May, several stations dropped below freezing including Mt. Carroll with 29 degrees.
The statewide average precipitation for May was 5.22 inches, 0.62 inches above normal. The precipitation was heaviest in the central third of the state (map) with a few drier areas around Bloomington and south of the Quad Cities. Areas in red received 5 to 8 inches of rain. Areas in shades of beige received between 2 and 5 inches of rain. Danville reported the most rain for the month in Illinois with 10.19 inches. The nearby station of Henning came in second in the state with 9.98 inches.
Widespread heavy rains were common in southern Missouri, Indiana, Ohio, and Kentucky as well.
Here is the same map, only showing the departures from normal rainfall. Areas in green and blue are above normal. Areas in blue are 2 to 4 inches above normal. Areas in yellow are 1 to 2 inches below normal. 
Can we expect more of the same for June? Yes, the latest June outlook from the NWS shows that the southern two-thirds of Illinois has an increased chance of being cooler than normal (left panel) and the southern half of Illinois has an increased chance of being wetter than normal (right panel).
