SPRINGFIELD — A prison watchdog group says the state’s mushrooming prison population is forcing some inmates to wait years for substance abuse treatment programs.

The Chicago-based John Howard Association says the Quinn administration’s decision to curtail a controversial early release program last year is causing fallout at the all-female Decatur Correctional Center.

With fewer inmates leaving the prison because Gov. Pat Quinn ended the controversial mandatory good time release program, long waits are now common for inmates wanting help with substance abuse, the group says.

According to the report, 120 inmates at Decatur are enrolled in a substance abuse program at the prison and a “staggering” 262 are on a waiting list.

“At more than double the enrollment, inmates can potentially spend years on the wait list before they are finally enrolled,” the report notes.

Deb Denning, chief of programs and support services at the Illinois Department of Corrections, said she is skeptical of the findings. She thinks waiting times may range from 60 to 90 days.

If inmates are locked out of one program, Decatur has other treatment programs and classes that can help inmates, she said.

“I feel very confident they’ve got access to programs,” Denning said.

For the over-populated prison system, the long wait for similar programs could have a ripple effect on the situation, the group notes.

Many inmates, for example, can earn time off for completing drug treatment programs. But because they must wait for openings, they cannot shave time off their sentences.

In addition, some inmates are required to undergo drug treatment as part of their sentences. In some cases, inmates must wait until after they are released from prison to join a program.

Corrections officials have been grappling with a rapid rise in overall population since the governor ended the early release program last year. The number of inmates now tops 48,500, up from 45,000 just two years ago. Decatur was built to house 500 inmates, but now holds more than 700.

The early release program was designed to free prisoners to reduce the inmate population, but some violent offenders were released in the process and went on to commit new crimes. The debacle became fodder during Quinn’s election bid against state Sen. Bill Brady, R-Bloomington.

Officials are studying how to revive the program in order to start bringing the prison population down to more manageable levels.

The association, which periodically surveys individual Illinois prisons, recommends the Illinois Department of Corrections expand substance abuse programs in order to reduce waiting times for inmates.