Monaghan is the county town of County Monaghan, Ireland. It also provides the name of its civil parish and barony.

The population of the town as of the 2016 census was 7,678. The town is on the N2 road from Dublin to Derry and Letterkenny.

The centre of the town is made up of four interconnecting squares: Market Square (or Street), Church Square, The Diamond and Old Cross Square.

Dating from the seventeenth century, the oldest remaining architectural feature in Monaghan town is the "Old Cross" - located in Old Cross Square. It is not fully agreed that it is in fact a cross, but may in fact have been a seventeenth-century sundial. It was originally located in the Diamond, the traditional centre of the town, and was used as a hiring cross and for the attaching of proclamations. It was moved to its present location in 1876 to allow for the construction of the Rossmore Memorial. Two landmark buildings remain from the eighteenth century, Aviemore House (built in 1760) on Mill Street and the "extremely elegant" Market House (from 1792) on Market Square.

Monaghan is notable for the quality of its nineteenth-century architecture, which adds a sense of dignity to the attractive town centre and its environs. Of its Victorian buildings, the Monaghan Courthouse on Church Square by Joseph Welland, which was built in 1830, is the most stately. With its sandstone facade of Doric columns supporting a pediment that bears the royal arms of the House of Hanover, Monaghan Courthouse constitutes an integral part of Church Square.

The Rossmore Memorial in The Diamond was built in 1876 as a memorial to The 4th Baron Rossmore, who died after a hunting accident at Windsor Castle in 1874. This Victorian monument, described by architectural historian C.E.B. Brett as "formidable and striking" is octagonal in shape, with central marble columns supporting a fountain. Around it, the eight grey columns support the pinnacled superstructure which rises to a dome. The dome is surmounted by a spire supported by yet more columns. The letters of Rossmore (also eight in number) are spaced out around the monument.

The Gothic-Revival St Macartan's Cathedral by J.J. McCarthy is recognised as being "one of McCarthy's best works: an excellent example of the High Victorian ecclesiastical style at its best, rich without ever being over-ornate". The building comprises a delicate rose window and an impressive soaring spire and took over thirty years to complete. Construction work began in 1861 and the cathedral was finally dedicated in 1892. Originally the nave was intended to be two bays longer but lack of funds meant that the design was cut back. The Cathedral sits on an imposing site overlooking the town. Occupying a similarly commanding site on the opposite side of the town is St Macartan's College for boys (from 1840), a 17-bay classical structure with a bell tower and private chapel, by the Newry-born architect Thomas Duff.

Church Square is very much an environment in which the civic pride of Victorian improvers lives on in the satisfying essay in the Ruskinian-Gothic style that is the Bank of Ireland building, as much as in the peaks of St. Patrick's Church of Ireland and the Dawson Obelisk. One of the most interesting aspects of Monaghan's Victorian architectural heritage, which also includes the former railway station, the Orange Hall on North Road and the Westenra Hotel on the Diamond, is the rounded corners that connect the town's buildings from one street or square to the next. This practice of rounding corners in order to open up panoramic vistas was carried out with unprecedented frequency in the town of Monaghan, and is still reflected today in the edifices of The Diamond, Church Square and Mill Street, helping to secure Monaghan's status as one of Ulster's more attractive large towns.