Wilson, writing in 1786, refers to Thornhill as the seat of Mr. Townsend. Two prooerties are shown in the townland of Derreendangan on the 1st edition Ordnance Survey map of the 1830s. One, Thornhill House, is described as "in ruins" while the other property, Thornhill Cottage, is located nearby. The townland was part of the estate of Thomas Uniacke at the time of Griffith's Valuation. The 25-inch map of the 1890s indicates Thornhill House again in use and there is a still a substantial farm at this site. Thornhill Cottage is no longer extant.