Built around 1606, this stone structure became the focal point of local commerce when Sir John Kingsmill was granted the manor of Castlefyn in 1631, complete with rights to hold a weekly Monday market and two annual fairs; one following Pentecost and another on St Martin’s Day in November, each lasting two days. The building’s most dramatic moment came during the Williamite War in 1688, when a spy named Scott, working for King William’s army, was captured by Jacobite forces and hanged from the market house’s southern arch, a grim reminder of the conflict that divided Ireland.

By 1836, when the Ordnance Survey memoirs were compiled, Castlefinn had grown into a bustling town of about 700 inhabitants, with the market house still serving as its commercial heart. The surveyors noted, with apparent disapproval, that whiskey shops vastly outnumbered all other businesses in the town, painting a vivid picture of 19th century Irish market town life. The building had received a new roof some twenty years earlier, ensuring its continued use as the town’s market venue, whilst also serving as a landmark for the daily mail coaches travelling between Londonderry and Sligo.

Today, the market house remains a prominent feature in Castlefinn’s diamond, the traditional name for the central square in Ulster towns. First officially mapped in the Ordnance Survey’s 6-inch series and still marked on modern OS maps, this enduring structure continues to anchor the town centre, standing as a tangible link to centuries of market days, political upheaval, and everyday life in rural Donegal.