Following John Howard's investigations into prison conditions two acts were passed in 1774: the first improved hygiene in prisons and allowed the appointment of prison doctors, the second abolished the practice of discharged prisoners having to pay gaolers on their release.

Inspired by Howard's reforms, justices in Denbighshire decided to build a new prison. By April 1774 Joseph Turner, architect of Chester, had drawn up plans; advertisements to carry out the work placed, and a committee appointed. Work began in January 1775. An inscription over the front door commemorates the building of the new prison:

THE MAGISTRATES,
SENSIBLE OF THE MISERABLE STATE
OF THE ANCIENT PRISON,
IN COMPASSION TO THE UNFORTUNATE,
CAUSED
THIS BUILDING TO BE ERECTED
IN THE YEAR
MDCCLXXV

Jos. Turner Architect

Life in gaol was harsh. A report into conditions dated 3rd March 1788 stated:

"COUNTY GAOL AT RUTHIN.
...No proper separation of the sexes... The debtors pay no chamber rent, and have the county allowance of two shillings a week, yet do not keep their rooms clean. One of the articles in the rules of 1785, is, that all prisoners committed for felony shall have irons put on their legs at the discretion of the keeper, and the same not be altered without the order of a justice of the peace'; even women are not excepted."