It became prosperous and its population grew as it became an important manufacturing and trading centre, both as a hub on the Great Northern Railway (Ireland) network and with its maritime link to Liverpool from the Port of Dundalk.

[6] The manor house built by Bertram de Verdon at Castletown Mount on the site of the earlier settlement is referred to as the "Castle of Dundalc" in the 12th century records of the Gormanston Register.

[11][12] The legends of Cú Chulainn, including the Táin Bó Cúailnge (The Cattle Raid of Cooley), an epic of early Irish literature, are set in the first century AD, before the arrival of Christianity to Ireland.

[19] There is a high concentration of souterrains in north Louth, particularly along the western periphery of the town including at Castletown Mount, which is evidence of settlements from early Christian Ireland.

[6] Archaeological and historical research suggests that before the arrival of the Normans, the district was composed of rural settlements of ringforts located on the higher ground that surrounds the present-day town.

[25] In about 1185, Bertram de Verdun, a counsel of Henry II of England, erected a manor house at Castletown Mount on the ancient site of Dún Dealgan.

In 1236, Nicholas's daughter Roesia commissioned Castle Roche, 8 km north-west of the present-day town centre, on a large rocky outcrop with a commanding view of the surrounding countryside.

The town was regularly attacked and was heavily fortified, with at least 14 separate assaults, sieges or demands for tribute by a resurgent native Irish population recorded between 1300 and 1600 (with more than that number being likely).

In 1600, the town was used as a base of operations for the English, led by Charles Blount, 8th Baron Mountjoy, for their push into Ulster through the 'Gap of the North' (the Moyry Pass) during the Nine Years' War.

The Royal Irish Army, who were led by the Duke of Ormond (and known as Ormondists), in turn, laid siege to Dundalk and overran and plundered the town in March 1642, killing many inhabitants.

The forfeiture of property and settlements carried out during the Restoration saw much of the land of Dundalk granted to Marcus Trevor, 1st Viscount Dungannon, who had fought for both sides in the civil war.

[38] After the end of the Williamite War, the third Viscount Dungannon, Mark Trevor, sold the Dundalk estate to James Hamilton of Tollymore, County Down.

[40] During the 18th century, Ireland was controlled by the minority Anglican Protestant Ascendancy via the Penal Laws, which discriminated against both the majority Irish Catholic population and Dissenters.

[42] In north Louth, the authorities had successfully suppressed the activities of the United Irishmen prior to the rebellion with the help of informants, and several local leaders had been rounded up and imprisoned in Dundalk Gaol.

The Irish National Land League held a demonstration in Dundalk on New Year's Day, 1881, stated by the local press to be the largest gathering ever seen in the town.

[48] Following the split in the Irish Parliamentary Party, the leading anti-Parnellite, Tim Healy, won the North Louth seat in 1892, defeating Nolan (who had stayed loyal to Parnell).

The campaign, predicted by Healy to be "the nastiest fight in Ireland", saw running battles and mass brawls in the streets between Parnellites, 'Healyites', and 'Callanites'—supporters of Philip Callan, who was trying to regain his seat.

[50] In 1910, on the accession of George V to the English throne, the local High Sheriff, accompanied by police and soldiers, led a proclamation to the new king at the Market Square.

[57] The accession of Ireland to the European Economic Community in 1973, however, saw factory closures and job losses in businesses that struggled due to competition, collapsing consumer confidence, and unfavourable exchange rates with cross-border competitors.

[70] As a result of the ongoing sectarianism in the north, there was sympathy for the cause of the Provisional Irish Republican Army and Sinn Féin, and the town was home to several IRA members.

[76] On 1 September 1973, the 27 Infantry Battalion of the Irish Army was established with its headquarters in Dundalk barracks, as a result of the ongoing violence in the border region of North Louth / South Armagh.

[86][87] The town's association football club, Dundalk F.C., first formed in 1903 by the workers of the Great Northern Railway, received European-wide recognition when it became the first Irish side to win points in the group stage of European competition in the 2016–17 UEFA Europa League.

The flat, low-lying coastal plain of the main part of the urban area consists of alluvial clays, laid down as the sea retreated following the last Ice Age.

It is represented at the national level in Dáil Éireann as part the Louth parliamentary constituency, which was created under the terms of the Electoral Act 1923, and first used at the 1923 general election.

The Dundalk Municipal District comprises all of the county to the north of a line running approximately east-to-north west, from the coast to the Monaghan border, across the villages of Castlebellingham and Knockbridge.

[117] In December 1929, the town council proposed to remove the "three black crows" seal because it had supposedly been imposed by King Henry VIII,[118] a historically inaccurate claim that met widespread derision.

[134] The town was slow to benefit from the Celtic Tiger economy that saw an economic boom in Ireland from the mid-1990s and continued to suffer from business closures and job losses.

[162][163] The neighbouring Louth County Infirmary (completed in 1834) was designed by English architect Thomas Smith in a neo-Tudor style with a central entrance-way flanked by two recessed ground floor arcades.

[191] Dundalk Institute of Technology (abbreviated to DkIT) is the focal point for higher education and research on the Belfast-Dublin corridor, serving the North Leinster, South Ulster region.

It was originally held at the Dundalk racecourse in Dowdallshill, before moving to the Fair Green, the grounds of St Mary's College, Bellingham Castle, and latterly Bellurgan Park.