Only one marked grave stands within the Idaho State Penitentiary’s main yard. First-time and return visitors alike will often refuse to call their visit complete without a stop near Dennis the cat’s headstone. In the years since his death, the black and white feline has “lived on” as a symbol of empathy and reverence for life within prison walls and become the unofficial mascot of the Old Idaho Penitentiary. Guests of all ages leave with Dennis lapel pins, shirts, or plush toys after visiting the Souvenir Confinement store, and one of the penitentiary’s most popular public events, Dennis the Cat Day, is held annually.

How did Dennis become such an “icon” of the Old Idaho Penitentiary? The site housed many working animals (and its share of wild creatures) in its 101 years of operation including crews of mouse-hunting kitchen cats, guard dogs and trail-sniffing bloodhounds, teams of horses, and many other animals whose names went unrecorded. In 1968, however, a prisoner named Ed Eline (#10691) writing for The Clock, the site’s prison-penned paper, eulogized Dennis with a written tribute and a caricature drawing that explained the prominent engraved headstone for future visitors. Unknowingly, Eline set the record for decades to come, paving the way for Dennis’ remembrance.

Adding to penitentiary legend, prisoners believed he was born on May 30, 1952, and passed away on the same date in 1968. Likely born near the chicken coops outside the prison’s main yard, a Magic Valley man serving time for robbery found the kitten and snuck him to his cell house where he and a cellmate cared for him until he earned his status as a beloved prison pet. Dennis grew fond of the “lifers” or long-term prisoners and spent much of his time in the boiler room keeping warm or sleeping on his countertop bed in the barber shop. According to Eline, “No cat in penal history ever claimed ownership of a prison more completely. The joint was his, and no one ever thought differently.” Yard games were paused as he passed through, and guards opened doors and gates for him to come and go.  

Dennis passed away peacefully in his sleep at age 16. In May 1968, the prison population held a solemn service in his honor, marking his on-site burial, much nearer to the main yard than the 2 Yard cemetery for prisoners. With such a visible presence on-site, marked by a headstone fashioned by prison residents, Dennis’ grave has become a landmark within the prison grounds. No known photographs exist of Dennis, only the illustration accompanying his obituary. While Old Idaho Penitentiary historians have preserved the stories of other prison animals and names wherever possible, the connection staff and visitors feel to Dennis remains the strongest. Dennis’ story speaks to the inherent kindness of individuals and the universal yearning for connection and companionship. 

CELEBRATE DENNIS’ BIRTHDAY WITH US!

Join us Saturday, May 23, for the sixth annual Dennis the Cat Day at the Old Idaho Penitentiary, marking the famous feline’s 74th birthday. Activities include games and raffles with prizes, vendors, “Prison Pets” history presentations, and more, with presentation admission offered with pet food donations, benefitting Simply Cats and the Idaho Humane Society. Ticket sales begin Tuesday, April 21. 

In late 2025, illustrators Susan E. Lasater and Veiko Valencia released, Dennis the Cat Was Here, a full-color all-ages paperback telling Dennis’ story. The Old Idaho Penitentiary is excited to premiere this book, available in the site’s gift store, with readings and more at this year’s event.