Chicago O'Hare Departures
O'Hare departures are often delayed for various reasons. Keep in mind that Chicago O'Hare is the world's second-busiest airport, and as such there's a ton of traffic that comes through O'Hare. If even one plane is off by a bit, it creates a ripple effect that slows everything down. A lot of things cause delays in O'Hare departures: weather, mechanical problems and traffic are the main issues.
You can use the official O'Hare flight tracker to check up on O'Hare departures, but it's recommended that you call the airline concerned to get the best information on the departure time.