During the 19th Century, hundreds of thousands of people were caught up in what Foucault famously referred to as the ‘great confinement’, or ‘great incarceration’, spanning reformatories, prisons, asylums, and more. Levels of institutional incarceration increased dramatically across many parts of Europe and the wider world through the expansion of provision for those defined as socially marginal, deviant, or destitute. While this trend has been the focus of many historical studies, much less attention has been paid to the dynamics of ‘the great decarceration’ that followed for much of the early‐ to mid‐20th Century. This article opens with an overview of these early decarceration trends in the English adult and youth justice systems and suggests why these came to an end from the 1940s onwards. It then explores parallels with marked decarceration trends today, notably in youth justice, and suggests how these might be expedited, extended, and protected.