Travelers also encountered weather-related delays at airports in the New York City area.
Flights in and out of O'Hare, the nation's second-busiest airport, were delayed by up to two hours, airport spokesman Gregg Cunningham said.
Chicago's Midway International Airport reported delays of up to 45 minutes, but did not report any cancelations.
The National Weather Service issued a dense fog advisory for northern Illinois Friday morning, and meteorologists said the low visibility would likely continue through Saturday morning.
Cloudiness was delaying arriving flights at New York's LaGuardia Airport and the Newark Liberty (N.J.) International Airport by an average of more than an hour late Friday, the Federal Aviation Administration said. The agency said the volume of traffic was holding up departing flights by an average of up to half an hour at Newark, but the delays were waning.
