Built during the late medieval period, likely in the 15th or 16th century, Knockmoylan Castle served as both a defensive structure and residence for local landowners. The tower house design was particularly popular amongst the Anglo-Norman and Gaelic Irish nobility, offering protection whilst demonstrating wealth and status in an often turbulent political climate.

The castle follows the typical tower house blueprint: a rectangular stone structure rising several storeys high with thick walls designed to withstand attack. These buildings usually featured vaulted ceilings on the ground floor for storage, with living quarters above accessed by a narrow spiral staircase built into the wall thickness. Windows were kept small and narrow on lower levels for defence, becoming larger on upper floors where the family resided. The battlements at the top provided both a defensive platform and commanding views across the surrounding farmland.

Today, Knockmoylan Castle stands as a reminder of Ireland's complex medieval history, when local lords needed fortified homes to protect their interests. Like many of Ireland's estimated 3,000 tower houses, it likely changed hands multiple times through conquest, marriage, and political upheaval before eventually falling into disuse. These structures offer valuable insights into how medieval and early modern communities organised themselves, defended their territories, and displayed their social standing through architecture.