This earthwork fortress consists of a roughly circular mound that rises 3.6 metres high, its flat summit measuring approximately 17 metres north to south and 14 metres east to west. The base of the mound spans about 24.5 metres at its widest point, creating the distinctive steep-sided profile typical of these medieval defensive structures.

Surrounding the motte is a broad, deep fosse; a defensive ditch measuring 4.6 metres wide and nearly a metre deep that would have provided an additional barrier against attackers. Interestingly, a later field bank now encloses this fosse on its southern side, showing how the landscape has been adapted and reused over the centuries. Unlike many motte-and-bailey castles of the period, no evidence of a bailey, the enclosed courtyard that typically accompanied these structures, remains visible at this site.

These earthwork castles were introduced to Ireland by the Anglo-Normans in the late 12th century as they established control over newly conquered territories. The motte would have originally supported a wooden tower or palisade at its summit, serving as both a defensive stronghold and a visible symbol of Norman authority in the landscape. Though the timber structures have long since vanished, the earthworks at Killanafinch continue to mark the medieval transformation of the Irish countryside.