A state Corrections Department spokesman said investigators unearthed the gun Thursday by cutting holes in a wall that was inaccessible to any of the prison's more than 1,900 murderers, rapists and drug dealers, the Bloomington Pantagraph reported.
"It was partially covered by mortar, gravel, dirt and other debris," department spokesman Tom Shaer said in a statement. "There was no ammunition present anywhere. Cement cutters and heavy-duty equipment were required in order to open the wall."
The newspaper said corrections officials had started looking for the weapon in 1996 after receiving a tip a gun had been smuggled into the more than 140-year-old prison.
"This led IDOC investigators to conduct various searches over 17 years," Shaer said. "All leads and intelligence were taken seriously and thoroughly investigated, even as much time passed with nothing found and no related problems.
"Recent intelligence that the weapon had been dumped inside the wall years ago led to this search."
He said the age of the weapon and its location in a wall that records show was last repaired in 2006 indicate it had been inside the prison for a long time.
"We stress that this weapon was introduced to the facility 17 years ago and that security measures have long since improved dramatically," he said.