From the early 14th century, Dungar served as the stronghold of the MacDermot Gall dynasty, Lords of Airtech and descendants of Dermot Gall, who briefly ruled as king of Moylurg from 1315 to 1316. Their influence began to wane during the 16th century, prompting Brian Mac Dermot of the Rock to construct or rebuild a fort here in 1565 for his son Rory, with permission from Mac Dermot Gall. By 1641, the castle had passed to Brian Mac Rory, and likely stood on the flat ground where Frenchpark House would later rise.

The French family, successful Galway merchants, began purchasing land at Dungar in the early 1600s and transformed the estate into something altogether grander. They erected a substantial house in 1667, as evidenced by dates carved into the pediment of what became an impressive seven-bay, three-storey brick residence. Around 1729, the property underwent significant expansion with the addition of two-storey wings; five bays by four, linked to the main house through elegant curving colonnades. This enhancement likely bore the hallmark of architect Richard Castle, who had also created the notable Strokestown House elsewhere in Roscommon.

Despite its architectural significance and centuries of history, Frenchpark House met an inglorious end when it was demolished in the 1950s. The site remains a testament to the shifting fortunes of Irish nobility and gentry, from the medieval Gaelic lords who first fortified the land to the merchant families who brought Georgian elegance to this corner of Roscommon, leaving behind only memories and historical records of what once stood here.