Idaho Maximum Security Institution

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Idaho Maximum Security Institution (IMSI) is a maximum-security prison near Kuna, Idaho. It is part of the South Boise Prison Complex, which includes seven facilities such as the Idaho State Correctional Center and the South Boise Women's Correctional Center. IMSI houses Idaho’s male death row and has the execution chamber. The prison opened in November 1989 to hold the state’s most dangerous offenders.

IMSI uses a double perimeter fence with razor wire, electronic detection, and 24-hour armed patrols. The facility houses many mentally ill inmates, including civil commitments, with about 30 beds for those with acute mental illness. Some beds are for administrative segregation and disciplinary detention, while others are for the close-custody general population. The prison’s capacity is 535 inmates.

It is managed by the Idaho Department of Correction. The current director is Bree Derrick and the warden is Randy Valley. In 2024, Security Journal Americas named IMSI as one of America’s Worst Prisons.