By the late sixteenth century people were imprisoned for non-payment of fines, vagrancy and debt. Often, the unconvicted awaiting trial were held with those already found guilty in crowded, unhealthy conditions. Men, women and children were imprisoned together and disease and immorality were rife.

In 1576 an Act enabled Houses of Correction or "Bridewells", administered by local justices of the peace, to be built where able-bodied idlers and the unemployed were sent and put to work.

Justices in Denbighshire were ordered by the judges of the court of Great Sessions to build the first county House of Correction in 1654 at Ruthin. Built at the bottom of Clwyd Street on the site of present gaol buildings, its first master Harry Davies of Ruthin, was appointed a year later.

In 1699 building additions led to the demolition of part of the town's ancient watergate.

"Pentonville Block" built 1866, before its recent renovation.