HMP Shepton Mallet, sometimes known as Cornhill, is a former prison in Shepton Mallet, Somerset, England. When it closed in 2013, it had been the United Kingdom's oldest operating prison, following the closure of HMP Lancaster Castle in 2011. Before closure, Shepton Mallet was a category C lifer prison holding 189 prisoners. The prison building is Grade II* listed, while the former gatehouse and perimeter walls are Grade II.