From Atlas and Cyclopedia of Ireland (1900)
NAME.—The town of Monaghan gives name to the county. The Gaelic form of the name is Muinechàn, a diminutive world signifying "little shrubbery," from Muinè, a shrubbery, with the diminutive affix can.
SIZE AND POPULATION.—Length, from the southeast corner near Ballyhoe Lake, to the northwest corner at Favor Royal, 38 ½ miles; breadth, from the southwest corner near Redhill, to the boundary east of Milltown, 22 miles; area, 500 square miles; population, 102,748.
SURFACE.—A part of the northwestern border is mountainous. That corner of the county northeast of Castleblayney is covered by a continuation of the Fews Mountains from Armagh. Nearly all the rest of the county is hilly, and may be described as a champaign country, broken up by a continuous succession of low hills, in some few places subsiding into an almost uninterrupted plain.
MOUNTAINS AND HILLS.—The Slieve Beagh range runs from southwest to northeast, and their southeast flank extends into Monaghan, occupying part of the northwest border of the county. The mountain Slieve Beagh itself lies in the adjacent counties, but it slopes into Monaghan. Eshbrack (1,190) stands just inside the boundary; and a mile further inward is Eshmore (1,103). The two mountains Essaglavane (1,196) and Essnaheery (1,078), slope into Monaghan, but their summits stand in Tyrone. All the preceding belong to the Slieve Beagh range.
Northeast of Castleblayney, near the eastern boundary, is Mullyash (1,034), which is one of the Fews range.
RIVERS.—The western part of the county is drained into the Erne; in this part the chief river is the Finn, which runs southwest, partly through Monaghan, partly through Fermanagh, and partly on the boundary, and joins the Erne near the head of Upper Lough Erne. Some of the headwaters of the Annalee River, which belongs to Cavan, come from Monaghan; the Bunnoe, for instance (see Cavan), rises to the east of Newbliss; another tributary, the Dromore River, comes from the cluster of lakes near Rockcorry; and a third, the Annagh River, coming from another chain of lakes near Shercock, has many of its feeders coming from the interior of Monaghan. The Blackwater (flowing by Moy and Charlemont into Lough Neagh), forms the northeast boundary for about a dozen miles, but never enters the county; near Glasslough it receives the Mountain Water, which runs eastward from the Slieve Beagh Mountains.
In the east, the County Water, flowing south from Tullynawood Lake, forms the eastern boundary (between Armagh and Monaghan) for 6 or 7 miles, then turning westward into Monaghan, it falls into Muckno Lake. In the southeast, the Clarebane, a short stream, runs from Muckno Lake to Ross Lake, the first mile being through Monaghan, and the next half mile—to Ross Lake —being on the boundary between Monaghan and Armagh; from Ross Lake, again runs the Fane, forming the boundary between Monaghan and Armagh for the first 4 miles of its course; next it runs through Monaghan for another 4 miles, after which it forms for a mile the boundary between Monaghan and Louth, and then enters Louth. In the extreme southeast, the Lagan River, after issuing from Ballyhoe Lake, runs northeast, and forms the boundary between Monaghan and Louth for 4 miles, after which it enters Louth; above Ballyhoe Lake its feeders come from the three adjacent counties, Monnaghan, Meath, and Cavan.
LAKES.—The lakes of Monaghan are very numerous. Beginning with the barony of Farney, at the southern extremity: on the south boundary is Ballyhoe Lake, the greater part of which belongs to Meath; near it is Rahans Lake, which touches Meath, but belongs to Monaghan; beside which is the small Descrat Lake, lying just inside the boundary; and northwest of this is Greaghlone Lake. In the interior of this barony; the beautiful Lough Fea, Lough Monalty, and Lough Bougagh, all lie near Carrickmacross; five miles north of which is Lough Nagarnaman.
In the south of the barony of Cremorne, and near the boundary of the barony of Farney, a chain of lakes stretches across the county. At the east is the fine lake of Muckno, containing 600 acres, with beautiful swelling shores and islets; near it on the south is Boss Lake, the greater part of which belongs to Armagh. West from this is Lough Egish, about a mile and a half in length. Still further west is Lough Morne, Shantonagh Lake, and Bellatrain Lake; and near the western border is Lough Bawn, Lough Derrygoony, and two sheets of water named Black Lough; north of which is Lough Avaghon; and near it, on the boundary with Cavan, Baraghy Lake.
Northwest of these, near Rockcorry, is a group of lakes close together; the largest is Inner Lake, which is wholly in Monaghan; beside which are Dromore Lake and Drumlona Lake, both on the boundary with Cavan; and near them, in the east, is White Lake, a mile from Rockcorry. Four miles west of Rockcorry are Annaghmakerig Lake and Drumgole Lake; and southeast of these, near the village of Drum, is Long Lake. In the western corner is the little Laurel Lake, and near it, on the border with Cavan, Drumcor Lake. Beside the town of Ballybay is the pretty Lough Major; two miles northeast of which are the two lakes of Corfin and Cordoo, beside each other.
Bound the town of Monaghan are a number of small lakes; among which are those of Cornaglare and Knockaturly, to the southwest of the town; the two lakes of Mullaghinshigo, to the northwest of Monaghan, beside Tedavnet; near which is Shee Lake; and east of these is Drumcaw Lake. Beside Glaslough, in the northeast, is the beautiful lake of Glasslough, which gives name to the village; and near it on the northwest is Emy Lough. On the northwest boundary is Lough More; southwest, still on the boundary, is the small Loughnaheery, at the base of the mountain Essnaheery. Near the western margin, at the base of the Slieve Beagh Mountains, are several small lakes, among which are Drumloo Lough and Kilmore Lough.
TOWNS.—Monaghan (3,369), the assize town, is a place of considerable trade. Clones (2,216), near the western boundary, occupying the summit of one of those round hills so numerous in that district, is a town of ecclesiastical origin, and of great antiquity, containing some very ancient church ruins and a round tower, and also a very large and conspicuous mound or fort. Four miles east of Clones is the neat village of Newbliss (404).
Near the southern extremity is Carrickmacross (2,002), with a brewery and a large distillery; containing also the ruins of a castle said to have been built by the Earl of Essex. Near the eastern boundary, beside Muckno Lake, is the neat town of Castleblayney (1,810); and near the middle of the county is Ballybay (1,654), in a pleasant valley, beside the pretty Lough Major.
MINERALS.—There is a small coal field southwest of Carrickmacross, a portion of the Ulster coal district; but it is not worked. Near the eastern border there is lead, but the working of the mines has been long discontinued.
ANCIENT DIVISIONS AND DESIGNATIONS.—In ancient times, down to the reign of Elizabeth, Monaghan belonged to the powerful family of Mac Mahon.
The present barony of Farney represents the old territory of Fearnmhagh or the Alder-plain; the barony of Monaghan is the ancient Hy-Meith-Macha; and the two baronies of Cremorne and Dartree represent the ancient Crioch-Mhughdhorna and Dartraighe.
At a place called Agha-Lederg, in the barony of Farney, a great battle was fought A.D. 331, which resulted in the destruction of the palace of Emania (see Armagh). The three Callas, brothers, sons of Ohy Dovlen, having slain their uncle the king of Ireland (Fiacha Sravtinnè), the king's son, Muredagh Tirech, banished them from Ireland, and became king himself. Some time after this they returned and became reconciled to their cousin the king, who supplied them with an army to make conquests for themselves. They marched to Ulster, and aided by a contingent from Connaught, encountered the Ulster king at Agha-Lederg; the battle lasted for seven days, and resulted in the defeat of the Ulstermen and the death of their king. One of the three brothers, Colla Menn, was slain in the battle. The two surviving brothers then destroyed the palace of Emania, which thenceforward ceased to be the residence of kings of Ulster; and they seized on a large part of Ulster, extending east as far as the Glenree River (flowing by Newry; see Down), which was from that time forth called the kingdom of Oriel.