Illinois experienced its wettest May – July on record with 19.69 inches of precipitation, 7.88 inches above the 20th century average, according to the National Centers for Environmental Information. Most of that was due to the record precipitation of June with 9.44 inches statewide, based on their latest numbers and discussed in more detail here.
Here is the time series of May – July precipitation in Illinois since 1895. The second wettest May – July was a tie between 1990 and 2010. And it was just three years ago, in 2012, when Illinois had its third driest May – July on record with only 5.60 inches (6.21 inches below the 20th century average).
Here is what the May – July 2015 precipitation departures from the 20th century average looked like for climate division in Illinois and surrounding states. That is about an extra two months of precipitation during that three-month period.