Elgin Fire Capt. Anthony Bialek (BYE-uh-lick) says a bathroom exhaust fan in a ceiling overheated and melted some wires and smoke was pushed throughout the facility's ventilation system.
The Federal Aviation Administration said all its personnel were evacuated from the Chicago Terminal Radar Approach Control, or TRACON, facility in suburban Elgin at around 11:30 a.m.
Bialek says it took about an hour to find the source of the smoke.
There were no injuries, and controllers have been allowed to resume their work.
Chicago Department of Aviation spokeswoman Karen Pride says she has not yet gotten word on whether flights have resumed.