The Union Workhouse was built at Thomastown, Merthyr Tydfil, in 1853; it was improved and enlarged in the 1870s and again in the early twentieth century, and a new infirmary was added in 1899. By 1920, it had accommodation for 450 inmates in the workhouse itself, and for a further 126 in the infirmary. In the early 1920s the name changed from 'workhouse' to 'poor law institution', and later to 'public assistance institution'; by the late 1930s it was known as 'Tydfil Lodge'. The institution became the responsibility of Merthyr Borough Council in 1930, and in 1948 became a National Health Service hospital under the name St. Tydfil's Hospital. The building still stands as a hospital, catering for geriatric patients.
There were several additional institutions: Pantyscallog House, Dowlais, accommodated elderly and infirm women from 1912/13; between 1915 and 1919 the Training School at Trecynon, Aberdare was adapted to become a subsidiary workhouse for adults and in 1920 Windsor House, Aberdare, opened to accommodate elderly and infirm men. Windsor House was situated in Llewellyn Street, Aberdare, on part of the subsidiary workhouse site.