For centuries, the residential tower attached to St Mary’s Church was mistakenly identified as this castle, but evidence suggests the true fortress stood elsewhere, likely near the present 18th-century Lucan House. The confusion arose from historical documents, including a 1702/03 claim by John Green at Chichester House for a property described as the ‘Castle, and great white house at Lucan’, which had belonged to Patrick Sarsfield, Earl of Lucan.

The castle’s documented history stretches back to at least 1534, when Sir William Sarsfield, then Mayor of Dublin, likely built it after acquiring the estate following the attainder of the 10th Earl of Kildare. A 1553-4 Crown lease to Matthew King provides fascinating details about life at the castle; the lessee was required to inhabit it with English-speaking men who dressed in English fashion and avoided communication with the Irish, reflecting the colonial tensions of Tudor Ireland. During the Commonwealth period, the Cromwellian Sir Theophilus Jones held the castle, which was described as one of the finest houses in County Dublin, boasting twelve hearths.

Archaeological surveys suggest the medieval castle may have stood beside a 17th-century gabled house, depicted on Down Survey maps, which was itself replaced by the current Lucan House in the 1770s. Some historians propose there may have been a second castle site on Main Street in Lucan village, adding another layer to this architectural mystery. Whilst the exact foundations of medieval Lucan Castle remain hidden, the tangled history of mistaken identities, property claims, and successive buildings on the site tells a compelling story of power, conquest, and architectural evolution in one of Dublin’s most historic settlements.