The Kentucky State Penitentiary (KSP), also known as the "Castle on the Cumberland," is a maximum security and supermax prison with capacity for 856 prisoners located in Eddyville, Kentucky on Lake Barkley on the Cumberland River, about 4.8 kilometres (3 mi) from downtown Eddyville. It is managed by the Kentucky Department of Corrections. Completed in 1886, it is Kentucky's oldest prison facility and the only commonwealth-owned facility with supermax units. The penitentiary houses Kentucky's male death row inmates and the commonwealth's execution facility. As of 2015 it had approximately 350 staff members and an annual operating budget of $20 million. In most cases, inmates are not sent directly to the penitentiary after sentencing, but are sent there because of violent or disruptive behavior committed in other less secure correctional facilities in the commonwealth. This was Kentucky's second penitentiary: the first was made uninhabitable from a flood in 1937.

A super-maximum security (supermax) or administrative maximum (ADX) prison is a "control-unit" prison, or a unit within prisons, which represents the most secure level of custody in the prison systems of certain countries.