Old Idaho State Penitentiary

The Old Idaho Penitentiary State Historic Site was a functional prison from 1872 to 1973 in the western United States, east of Boise, Idaho. The first building, also known as the Territorial Prison, was constructed in the Territory of Idaho in 1870; the territory was seven years old when the prison was built, a full two decades before statehood.

From its beginnings as a single cell house, the penitentiary grew to a complex of several distinctive buildings surrounded by a 17-foot-high (5.2 m) sandstone wall. The stone was quarried from the nearby ridges by the resident convicts, who also assisted in later constructions.

Less than two miles (3 km) southeast of downtown Boise and near Table Rock, the Old Idaho Penitentiary is operated by the Idaho State Historical Society; the elevation of the site on Warm Springs Avenue is approximately 2,770 feet (845 m) above sea level.

Dennis, a kitten found in the prison barn by an inmate in 1952 was kept in the penitentiary for sixteen years. Guards allowed him to keep Dennis even though incarcerated men were not allowed pets. Dennis roamed the yard and made friends. The guards and inmates grew to love him. In 1968, Dennis died in his sleep. The inmates performed a funeral in his honor, even providing him a headstone. Dennis is the only "inmate" buried within the prison walls.