The essay deals with Alexis de Tocqueville's writings on the prison system, paying special attention to Le système pénitentiaire aux Etats-Unis et son application en France. These writings have been overlooked for a long time and are still disregarded by many readers of Tocqueville. I instead argue that they should be taken into consideration, since they offer a significant point of view on Tocqueville's political thought, revealing how, paradoxically, the "democratic prison" has been organized as the reverse of democracy.