American Airlines said its computers were back online after experiencing a widespread outage on Thursday, according to NBC affiliate WMAQ.
The company later took to Twitter to announce the problems had been resolved.
The Federal Aviation Administration first reported the outage and said only that the cause of the ground stop was "airline issues."
The airline also responded to customers amid the outage, but did not specify what caused the outage.
American's stock was up about 2.5 percent in afternoon trading.
Computers at O'Hare reportedly started to come back online mid-afternoon, and only 10 departures had been delayed, WMAQ said.
Earlier, the airline told the NBC affiliate that it was working on resolving the issue and that it did not know how long it would take to resolve.
A company spokesman had told Reuters that all domestic flights departing from Dallas-Fort Worth, Chicago O'Hare and Miami had been halted.
Correction: An earlier version of this story misstated the name of NBC affiliate WMAQ.