Dennis the Cat Day 2026

Dennis the Cat Day is coming up on Saturday, May 23!

Join the Old Idaho Penitentiary in discovering and celebrating the story of the penitentiary’s historic animal mascot, Dennis the black and white tuxedo cat, during our sixth annual Dennis the Cat Day!

Activities include Prison Pets history presentations, Prison Paws scavenger hunt, games (such as Pin the Tail on Dennis), and more! Music, food trucks, beer and alcohol, local pet supply vendors, new Dennis merchandise, and more will be available! Vendors include Wild Frontier Beer Project, Pizza Piou, Big Beantz Taco Co., For the Love of Lemons, and City Peanut Shop (with their special Dennis the Cat Mix on hand)!

Be sure to bring donations of unopened pet food for admission to the Prison Pets history presentations! Donations benefit the Idaho Humane Society and Simply Cats. Presentations take place at 12:30, 1:30, and 2:30.

The site will also be celebrating the release of the new full-color picture book, Dennis the Cat was Here, by illustrators Susan Lasater and Veiko Valencia (with original text by penitentiary resident Ed Eline). Join the illustrators for readings at 1:15 or 2:15 pm.

Dennis the Cat Day: Saturday, May 23, 12:00 pm – 5:00 pm (last admission 4:00 pm). All ages welcome. Register at the door or online at history.idaho.gov/events.

Idaho State Historical Society Members receive free admission to this event! Learn more and become a Member at history.idaho.gov/membership. Members must bring pet food donations for presentations.

Between 1952 and 1968, Dennis lived among the staff and residents of the Idaho State Penitentiary, becoming one of the site’s best liked and most respected figures. Upon Dennis’ death in 1968, the prison population buried him nearby within the main yard, fashioning a durable engraved headstone marking his resting place during his funeral services. Today, guests of the Old Idaho Penitentiary regularly pay their respects at his stone, the only marked grave within the prison walls.