HEYNSTOWN, or HAINSTOWN, a parish, in the barony of UPPER-DUNDALK, county of LOUTH, and province of LEINSTER, 2½ miles (S.) from Dundalk, on the road to Ardee; containing 442 inhabitants. This parish comprises, according to the Ordnance survey, 1980½ statute acres, which are chiefly under tillage. It is well planted, and the scenery is highly picturesque; there is an abundance of good building stone. Prospect, the seat of W. H. Richardson, Esq., commands a very extensive view; and Clermont Park, that of T. Fortescue, Esq., stands in a handsome and well-wooded demesne, comprising about 800 statute acres. The living is a rectory, in the diocese of Armagh, and in the patronage of the Lord-Primate: the tithes amount to £350; there is neither glebe-house nor glebe. The church is a plain modern structure, near which are some remains of an ancient round tower. In the R. C. divisions the parish forms part of the union or district of Haggardstown, at which place is the chapel. Here are the ruins of Dunmahon castle, consisting of a quadrangular pile, with circular towers of dissimilar sizes at the angles.
from Lewis's Topographical Dictionary of Ireland, 1837.