What’s the most rainfall Chicago has received from a single thunderstorm?

Dear Tom,
What’s the most rainfall Chicago has received from a single thunderstorm?
— Martin Nenov, Des Plaines
Dear Martin,
The Chicago area has been hit by numerous blinding downpours, but Chicago weather historian Frank Wachowski quickly pinpointed the worst. On the afternoon of June 10, 1967, a severe thunderstorm swamped the Loop with 6.09 inches of rain — 5.20 inches of it falling in just two hours, while O’Hare and Midway airports both received about 3 inches. The storm brought widespread flooding, with high water closing area expressways. In addition, a tornado tore roofs off of homes in Romeoville, and high winds caused damage at Galt Airport in McHenry County. Thousands of residents were left without power. A close runner-up was the thunderstorm that spawned the Lemont tornado on June 13, 1976, delivering 4.29 inches in just two hours.