The site first appears in historical records as Tonregie, featured in Captain Nicholas Pynnar’s 1619 survey of Ulster plantations. This early fortification boasted impressive defensive features: a vaulted castle protected by a 90-foot square bawn and two flanking towers, designed to withstand the uncertainties of plantation-era Ireland.

The castle as it stood for centuries was the work of William Baillie, a Cromwellian planter who arrived in the mid-1600s during one of Ireland’s most turbulent periods. Baillie either incorporated the existing Tonregie fortification into his plans or built atop its foundations, creating what became known as Bailieborough Castle. His timing was significant; Cromwellian planters like Baillie were part of a massive redistribution of Irish land following the Confederate Wars, fundamentally reshaping the social and political landscape of counties like Cavan.

The castle remained a prominent feature of the local landscape for nearly two centuries before meeting an ignominious end. Sometime before the 1830s, the ancient structure was demolished to make way for additions and improvements to a more modern house on the site. Lewis’s Topographical Dictionary of 1837 notes that the castle had only recently been pulled down, its stones repurposed for contemporary building projects; a common fate for many of Ireland’s medieval and early modern fortifications during the Georgian and Victorian periods when ancient ruins were often seen as convenient quarries rather than historical treasures.