Any Transfer desk can help, there are boards with all departures along the walkway to all gates. You canl check online to at flyohare
If the flight is a US carrier that departs from the same domestic terminal, (E.g. an AA flight arriving from Dallas and departing from Terminal 3 to Heathrow) merely make your way to the appropriate gate. If your flight departs from the international Terminal (e.g. a British Airways flight to Heathrow) you'll need to take the ATS (airport transit system) to Terminal 5 and then clear security again. Note that there is no TSA Pre-Check in Terminal 5.
Check on any departure monitors the number of your flight or just the city and time where u r flying to. If not ask help desk. You can also download an app on O'Hare airport on ur cellphone
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