Poor Law Unions - Clwyd FHS The Workhouse  - on Peter Higginbotham's site

The records of the Holywell and St. Asaph poor law Unions, from 1837 to 1930, are held at Flintshire Record Office. They include registers of admissions and discharges, and of births and deaths. The records of the Hawarden Union, from 1853 to 1930, are also at the Record Office, but they are much less complete.

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.