Yet that unremarkable building is one of the last physical traces of a Union Workhouse, the kind of institution that shaped, and in many cases ended, the lives of thousands of people across Ireland during the nineteenth century. The rest of the original complex was largely demolished in the 1950s and replaced by the modern hospital blocks that dominate the site today.

The workhouse at Kilknockan first opened in 1842, and its layout at that time followed the standardised form prescribed under the Irish Poor Law system: a gatehouse and an H-plan block set within a rectangular enclosure measuring roughly 120 metres by 70 metres. Union workhouses, built to designs approved by the Poor Law Commissioners, were intended to house the destitute poor in conditions deliberately kept austere, on the principle that the prospect of entering one should deter all but the genuinely desperate. The 1842 Ordnance Survey six-inch map records the site plainly as "Union Work House", and much of that original plan was still visible on the equivalent map of 1935. What survives today is the south-western arm of the H, a long two-storey structure with irregular window openings and external stairs rising along both end walls to first-floor doors. A short stretch of the boundary wall survives to its rear. Just to the north-west stands a separate two-storey Fever Hospital, nine bays long with a bluntly pointed central doorway and single-storey outbuildings at the back. It opened in 1847, the second year of the Great Famine, replacing an earlier fever hospital on a hill roughly 800 metres to the south-east. The timing of its construction speaks plainly to the conditions that necessitated it. Along the south-eastern side of the complex runs a further two-storey range, fourteen bays in length, built over a basement in random-rubble limestone with flat-arched window openings, dating in appearance to the mid or late nineteenth century.