CHICAGO — The Illinois Department of Corrections is shelving plans to shutter a maximum security unit in Joliet, targeting a more than 130-year-old prison in Pontiac for closure instead.

Many Pontiac Correctional Center inmates would move to a new-but-never-used maximum facility jailhouse in Thomson in northwestern Illinois’ Carroll County, according to a letter from Corrections chief Roger Walker Jr., that was released Monday.

Gov. Rod Blagojevich said in February he wanted to close a portion of the Stateville Correctional Center in Joliet to save millions in operating and remodeling costs at the 83-year-old prison, but the plan met with stiff resistance. This latest proposal to close Pontiac is guaranteed to meet with opposition too. There was an unsuccessful move in 2004 to try to close Pontiac, which first opened in 1871.

“We are going to fight very hard to keep Pontiac open,” said American Federation of State, County and Municipal Employees Council 31 Executive Director Henry Bayer.

The proposed closure would affect about 550 employees at Pontiac, which has more than 1,600 inmates, said Sergio Molina, executive assistant to Walker.

Thomson is a newer prison that also meets the department’s need for single cells, Molina said.

Closing Pontiac would be devastating to central Illinois because it’s “a major, major employer,” said Republican state Sen. Dan Rutherford.

“They’re whipsawing these communities and it’s inappropriate,” Rutherford said.

Walker said it’s essential the state use its new Thomson prison.

“I have been clear in expressing the challenges we face in the operation and management of our maximum security facilities. They are some of the oldest in the country,” Walker wrote in a May 2 letter to state Sen. A.J. Wilhelmi, D-Joliet, a vocal opponent to closing part of Stateville.

Completed in 2001, Thomson has about 1,600 single maximum-security cells that have not been used, Molina said.

Some minimum security prisoners are at Thomson.

“We believe this is a good proposal that will help us maintain a safe and secure operation,” Molina said.

Wilhelmi cheered the decision to not shutter part of the Joliet prison.

“I vowed to the workers of this prison and their families that I would halt this disastrous closing and put all I’ve got into keeping Stateville open,” Wilhelmi said in a statement Monday.

Senate President Emil Jones said it makes sense to close old prisons when the state has new prison space sitting idle.

“It’s a safety issue. Then, too, I do understand the concerns of the community because they look at it as an economic tool. ... It’s a very delicate question,” Jones said.

But Rutherford said it makes no sense.

“I see absolutely no reason to close Pontiac if your intention is to try to relieve the overcrowding of our prisons,” he said.