Llanrwst Poor Law Union records 1837-1903  - details of extant records on Archives Network Wales

Poor Law Unions - Clwyd FHS

The Workhouse  - on Peter Higginbotham's site

The Poor Law Amendment Act of 1834 introduced a system of poor relief based on unions of parishes, which were run by boards of guardians. The Civil Registration districts created in 1837 were based on the poor law unions, and full details of the structure of each union in Denbighshire may be seen on the "historic" Registration Districts page.
There were three unions based within Denbighshire, namely Llanrwst, Ruthin and Wrexham; although both Llanrwst and Wrexham included "out of county" parishes. Conversely, a number of Denbighshire parishes were included in "out of county" unions - Conwy, Corwen, Llanfyllin, Oswestry and St. Asaph.
The records of the Ruthin, Llanrwst and Wrexham poor law Unions, from 1837 to 1930, are held at Denbighshire Record Office. Unfortunately, many of the records for the Ruthin union were destroyed prior to the demolition of the Ruthin Workhouse. Further details on post 1834 workhouse/Union records  for Conway, Corwen, Llanwrst, Ruthin, Wrexham and St Asaph can be found on the Denbighshire Archives website
The records for Conwy Union from 1867-1929 are held at Denbighshire Archives. Details are shown on the JISC website.
The records for Llanfyllin Union are held at Powys Record Office, Llandrindod Wells.
The records for Oswestry Union are held at Shropshire Archives Shrewsbury.
 

The Workhouse  - on Peter Higginbotham's site

Hospital Records Database   A Joint Project of the Wellcome Trust and the National Archives. This database provides information on the existence and location of the records of hospitals in the U.K. Currently over 2,800 entries can be found by searching the database

Index to "Paupers in Workhouses in England & Wales in 1861" (10% sample)

• Peter Higginbotham's comprehensive The Workhouse website provides a wealth of information about Workhouses, the Poor Law and related issues.catalogue
• If you are looking for someone who was in a workhouse, it is worth checking if they also appear in the Quarter Sessions records, held in County Record Offices - see the British Library's Discovery catalogue (use Advanced Search and select "Search Other Archives"). 
• You can search and freely download documents of a number of Poor Law Unions across England and Wales from TNA.
• Settlement Examinations in England and Wales - a detailed explanation, from LDS Familysearch, based on an article by Anthony Camp.