The July 2023 Chicago Area Flood was caused by a heavy rainfall that occurred on July 2, 2023, in the Chicago Metropolitan Area of northeastern Illinois. Rainfall up to 9.0 inches (23 cm) occurred over an 18-hour period; the majority occurred from early in the morning to late in the afternoon.[1] Flood-related damages across northeastern Illinois were estimated to be at least $500 million (equivalent to $500 million in 2023[2]) in the Chicago area, making it among the most expensive weather-related events in the history of Chicago and Cook County.[1] This event was part of a cluster of three extreme rainfall events which occurred in the central portion of the metropolitan area within an approximately one-year period from September 2022 to September 2023. The flood event occurred on the same day as the NASCAR Grant Park 220 on the Chicago Street Course.