GLASSLOUGH, a post-town, in the parish of DONAGH, barony of TROUGH, county of MONAGHAN, and province of ULSTER, 5 miles (N. E.) from Monaghan, and 70¾ (N. W.) from Dublin; containing 812 inhabitants. It is situated on the road from Monaghan to Caledon, on the margin of a beautiful lake, whence the town derives its name, signifying "the green lake." It has a striking and attractive appearance, and contains excellent slated houses. It is favourably situated with regard to commerce and agriculture, but until a very late period had little or no trade. In consequence of the judicious modes which have been adopted by the present owner, Mrs. Leslie, its capabilities have been developed and it has shown decided symptoms of rapid improvement. It has now a weekly market for wheat and flax, and a fair on the third Friday in every month for cattle, sheep, pigs, and other agricultural produce. An extensive flour-mill has been lately built in the neighbourhood, for which an ample supply of wheat is obtained from Glasslough market; and mills are now being built for scutching and spinning flax, also a factory on a large scale for weaving linens by hand and power looms; the whole, when completed, will afford permanent employment to between eight and nine hundred individuals. The beautiful and extensive park and castle of Mrs. Leslie, which adjoins the town and contains upwards of 1000 acres of fine land well planted, adds much to the natural beauty of the situation. The mansion was originally of considerable grandeur, but in consequence of repeated alterations has lost all its antique features. The ancient castle was situated opposite to the town gate of the present house, and was a building of considerable strength, flanked with circular towers and defended by a moat and drawbridge, possessing also those indispensable requisites of feudal power, a keep and donjon. The site had been a place of strength long before its erection, and was granted to O'Bear McKenna by O'Nial of Ulster, on the conditions that he and his descendants should pay "Bonaghty," or tribute, and furnish white meat and oats to the Gallowglasses of O'Nial on certain days when they visited the holy well of Tubber Phadrick, near Glennan, and never to wage war with the O'Nials. This tribute was paid at stated periods in a house built of wood and osiers, at Anaghroe, or the "Red River," now the seat of William Murdoch, Esq. Near the town is the hill and rath of Drumbanagher, where, on the 13th of March, 1688, a battle was fought between a detachment of the Irish army, on its way to join the besiegers of Londonderry, and the native Protestant forces of the district, in which the latter gained a complete victory, but with the loss of their gallant colonel, Matthew Anketell, to whose memory a monument was erected in the parish church, which is still preserved. In the town is the parish church, with a tower 130 feet high: it has nothing in architectural beauty to attract notice; the interior arrangements are plain, neat, and commodious. During the erection of the tower a workman fell from the top, but escaped without suffering any material injury.
Transcribed from A Topographical Dictionary of Ireland, 1840 by Samuel Lewis