That was a bit mis-worded ... 25 inches is normal in a Tropical Storm ... the Upper Midwest doesn't get Tropical Storms ...
17 inches in a day in Illinois ... "The Chicago Tribune called the city's [July 18th] 1996 rainstorm the second greatest Illinois natural disaster while noting "the deluge in Aurora was considered a 1-in-1,000-year event." Eight residents died during the torrential rains, and almost half of the homes in Aurora flooded. The one-day storm caused an estimated $600–$700 million in damage." {
Cite} ...
The point is ... if it's happened before, then it's not "unprecedented" ... 42 inches in a single day ... see the above citation ...