As is the case for most large US airports 3 hours before an international flight and 2 hours before a domestic flight is good advice. At O'Hare these suggestions might actually have you waiting around some time for your gate to open but specific busy times, delays and winter weather can mean you'd be well served to follow those guidelines. O'Hare tends to be busiest early mornings, mid to late afternoons and Mondays and Fridays. To check for journey times to the airport click here.
You can view the availability of TSA PreCheck at the O'Hare terminals by looking at the table above.
For information on joining TSA PreCheck and reducing your O'Hare Airport security wait times visit https://www.tsa.gov/precheck.
Most international arrivals will process only through Terminal 5. Consequently it can mean O'Hare security wait times for non-US citizens arriving here can be lengthy. For those with connecting flights it is worth knowing that if you are arriving at O'Hare during busy periods you should ensure you have plenty of time between arrival and your connecting flight out of ORD as you could be stuck in a security line for north of an hour or more.
For further information on Chicago O’Hare Airport wait times, TSA, airport wifi, ground transportation, lost and found and more visit https://www.flychicago.com/ohare/home/pages/default.aspx.