No walls, no foundations, no obvious trace of a house that once served as the centre of a substantial landed estate. What exists instead is a geophysical ghost: the faint subsurface outline of a T-plan house, roughly 22 metres by 14 metres, sitting within a rectangular enclosure, detected only through a survey conducted as part of doctoral research by Dr. Siobhán McDermott at NUI Galway. The signals were so weak that the house may never have been built in stone at all, but rather of timber, leaving behind little more than soil anomalies and a cluster of back-filled pits that were probably once cellars.

The estate at Derrynashallog was built up by Oliver Anketill, a grandson of Christopher Anketill of Shaftesbury in Dorsetshire, who came to Ireland in the mid-seventeenth century and began acquiring land in north Monaghan, likely by purchasing the interests of Undertakers and soldiers, the category of English and Scottish settlers who had received grants under the Ulster Plantation. Oliver died in 1666, and in 1667 some 3,300 acres across seventy townlands in the barony of Errigal Trough were confirmed to his son Mathew. The townland of Derrynashallog itself had been in the hands of a Gareth Rooney as recently as 1640 before becoming the core of what the family called Anketill's Grove. It was probably Oliver's grandson, also named Oliver, who actually built the house here; he served as sheriff of Monaghan in 1710 and as an MP for Monaghan town in 1759 to 1760, dying in 1760. Within two decades the house was gone. His grandson Mathew pulled it down in 1781 when the family relocated to a new Anketell Grove at Gortmoney, about 1.5 kilometres to the south.

The cartographic record of the site is its own small puzzle. Taylor and Skinner's map of Irish roads, published in 1778, already marks Anketill Grove at Derrynashallog as a ruin, three years before Mathew is said to have demolished it, while McCrea's map of the Barony of Trough from 1793 shows it as a roofed house, a full decade after the supposed demolition. The Ordnance Survey six-inch map of 1834 ignores the house entirely but does record the designed landscape that surrounded it, including a formal avenue climbing the drumlin slope from the north-east, in the direction of Emy Lough, which leads to where the geophysical survey later placed the house and its enclosure.