St Asaph Poor Law Union was formed on 10th April, 1837. Its operation was overseen by an elected Board of Guardians, 24 in number, representing its 16 constituent parishes.

The population falling within the Union at the 1831 census had been 22,017 with parishes ranging in size from Llandulas (population 307) to Denbigh (3,786). The average annual poor-rate expenditure for the period 1834-36 had been £11,431 or10s.5d. per head.

St Asaph Union workhouse was erected in 1838-9 to the south of St Asaph. The Poor Law Commissioners authorised an expenditure of £5,499.16s.8d. on construction of the building which was intended to accommodate 200 inmates.

The workhouse design, by John Welch, followed the popular cruciform or “square” layout with separate accommodation wings for the different classes of inmate (male/female, infirm/able-bodied etc.) radiating from a central hub.

In 1847, the five-year old orphan John Rowlands became an inmate of the workhouse. In later life in the USA, Rowlands adopted the name Henry Morton Stanley and, as a journalist for the New York Herald, tracked down the missing explorer Dr David Livingstone, greeting him with the famous words “Dr Livingstone, I presume?”

After 1930, the workhouse became St Asaph Public Assistance Institution. From 1910 until 1948, the St Asaph Infectious Diseases Hospital also operated on the site.

Services at the hospital ended in April 2012 and the site was sold for redevelopment in January 2013.