The first House of Correction, or Bridewell, was built at the bottom of Clwyd Street, next to the river, in 1654, to replace the Old Court House, where able-bodied idlers and the unemployed were sent to work. Following John Howard's investigations into prison conditions the Denbighshire justices resolved to build a new model prison in Ruthin on the site of the old Bridewell. Work began in January 1775. In 1802 the prison had four cells for prisoners and nine rooms for debtors. By 1837 it could hold 37 inmates.
The Prisons Act of 1865 set new standards for the design of prisons — as the Ruthin County Gaol did not meet the standards plans were drawn up for a new four-storey wing, and the new prison accommodating up to 100 prisoners, in the style of London's Pentonville Prison was built at a cost of £12,000. On 1 April 1878 the Ruthin County Gaol became HM Prison Ruthin, covering the counties of Denbighshire, Flintshire, and Merionethshire.
As far as is known, only one person was ever executed in the prison, William Hughes of Denbigh, aged 42, who was hanged on 17 February 1903 for the murder of his wife, his plea of insanity having failed. Another colourful prison personality was John Jones, known as Coch Bach y Bala – who was a kleptomaniac and poacher who had spent more than half his 60 years in all the prisons of north Wales and many in England; he twice escaped from Ruthin Gaol, first on 30 November 1879 when he walked out of prison with three others while the staff were having supper — a £5 reward was offered for his capture, which happened the following 3 January.
On 30 September 1913 he tunneled out of his cell and using a rope made out of his bedding he climbed over the roof of the chapel and kitchen and got over the wall; after seven days living rough on the Nantclwyd Estate several miles away, Jones was shot in the leg by one of his pursuers, 19-year-old Reginald Jones-Bateman. Jones died of shock and blood loss, while Jones-Bateman was charged with manslaughter, though the charges were subsequently dropped.
