The fire broke out in the old Joliet Correctional Center at 1132 Collins Street overnight. There was no word of injuries, but residents say they saw flames coming from the prison around 3:30 a.m.
One witness says flames were 70 feet high. Lockport and East Joliet firefighters are at the prison assisting.
One witness and a firefighter say break-ins and squatters have been reported at the prison in the past. There's still no word on a cause.
The road is closed in front of the jail.
The prison opened in 1858 and closed in 2002.
"It was just shock and awe. I lived here all my life here on the same block and I pass by there every day. It is amazing how big the fire was. It was just -- and at 3:30 in the morning, it was dark. You could see it. It was humungous," said witness Eddie Rodriguez.
Randich says the call came in about 3 a.m. from someone who could see the flames three miles away.
"When the crews first arrived on the scene, there was heavy fire through a structure that was -- there is approximately 12 to 15 structures inside this facility. This was the first building," said Randich.
Randich says prison personnel told him the building is 90 years old and was previously used as a mattress factory, but is now an empty warehouse sometimes used as a training facility. The prison is often used for military training.
Fire officials say none of the well-known structures were damaged.
The state fire marshal is investigating, since there was no electricity at the time of the fire.
"We're gonna take an additional look at the back gates to make sure that they can't be compromised and to try to determine if someone did gain entry," said Tom Shaer, Illinois Department of Corrections.
Locals, such as Michelle Witte, think the old building should be turned into a ghost museum instead of sitting empty.
"I think that if they really did put a museum, something ghost, that people will come," she said.
The Associated Press contributed to this report.