The oval mound, measuring roughly 29 metres at its base and rising just over 3 metres high, contains scattered masonry rubble that hints at its former status as a fortified residence. Historical maps from 1837 show it was once a small rectangular castle, about 10 metres square, positioned at the northwest corner of what may have been a defensive bawn enclosure measuring approximately 45 by 40 metres.

The castle’s history stretches back to at least the late 15th century, when the Dillon family, descendants of Sir James Dillon of Proudstown in County Westmeath, established themselves at Curraghboy. Margaret Dillon, daughter of Robert Dillon of Curraghboy, strengthened local alliances by marrying Cormac Mac Dermot sometime between 1499 and 1528. By 1580, Thomas Dillon held the castle, maintaining ownership through the 1590s. Though absent from the Strafford map of circa 1636, which instead marks a castle at nearby Killcarne, the site remained significant to the Dillon family well into the 17th century.

Richard Dillon controlled the town of Curraghboy and over 250 acres across three quarters of land there in 1641, holdings he retained through the turbulent 1660s. While some early accounts suggested the castle might have been built by the O’Kelly family, the Dillons’ long tenure shaped its history for nearly two centuries. Today, visitors to the site find only the earthwork remains of what was once a strategic stronghold, its grassy slopes offering little indication of the political and familial power it once represented in medieval and early modern Roscommon.