Dozens of firefighters, first responders were seen around 1 p.m. at the Illinois Youth Center in Warrenville on Ferry Road.
The Illinois Department of Juvenile Justice said the flames and smoke left significant damage.
First responders were seen breaking part of a roof where the smoke was coming out of.
Some firefighters were seen taking breaks under trees as the heat index in the high 90s.
One person was taken to the hospital for smoke inhalation.
It's unknown what caused the fire.