The Ordnance Survey of 1840 noted the ruins of an ancient castle adjoining what was then the residence of R. Ievers, Esq. Today, visitors can see a four-bay, two-storey country house built around 1830, complete with a central breakfront and portico facing west. What makes this site particularly intriguing is the late medieval castle attached to its rear elevation, featuring rubble limestone walls crowned with cut limestone crenellations and a stringcourse running beneath them.

The history of Tullerboy Castle stretches back to at least 1319-20, when it was known as Tylahorwy and held by John de Kerredyn before being granted by the King to the Bishop of Ossory and his heirs. The castle changed hands numerous times over the centuries; in 1583, Edmund Leo held Tollerboye, though the previous owner, W. Ryurdane, had been killed during Desmond’s rebellion. By the 1650s, Walter and Morras Leo, described as Irish Papists in the Civil Survey of Limerick, owned the property, which then consisted of a castle, a bawn (fortified enclosure), a thatched wall stone house, and another dwelling. The tower house appears on 17th-century Down Survey maps of both Coshma Barony and Ballingaddy Parish, testament to its local importance.

Architecturally, the castle has been classified as a Type 4 tower house, representing the final phase in the Irish tower house tradition. These later examples display sophisticated defensive features including tourelles equipped with shot holes, hood-moulded and mullioned windows, parapet water spouts, and cruciform roofs; all elements that speak to the evolution of defensive architecture in late medieval Ireland. The juxtaposition of the Georgian mansion with its medieval predecessor creates a unique architectural dialogue, where centuries of Irish history stand side by side in stone and mortar.