From the Prospect Heights Fire District:

The Prospect Heights and Wheeling fire departments were called to Chicago Executive Airport at 11:01 a.m. for an incident involving a small aircraft. Specialized Aircraft Rescue and Fire Fighting apparatus responded along with other fire apparatus and ambulances. The aircraft registration number is N99715 and is a Cessna 172P Skyhawk II. During a takeoff or landing, the single-engine plane left the runway at the north end of the airport and came to rest nose-down in the grass. There was a small fuel leak. No one was injured. The pilot was the only person onboard. The FAA and NTSB were notified of the incident.