Dundalk is the county town and administrative capital of County Louth in Ireland. It is situated where the Castletown River flows into Dundalk Bay. The town is close to the border with Northern Ireland and equidistant from Dublin and Belfast. The town's name, which was historically written as Dún Dealgan, has associations with the mythical warrior Cú Chulainn. The town's crest reads Mé do rug Cú Chulainn Cróga, meaning "I gave birth to brave Cú Chulainn". It was granted its charter in 1189. Within Legal Town boundary limits it is the largest town in Ireland having an urban population in 2011 of 31,149, however with the inclusion of environs it is the second largest town and seventh most populous urban area with a population in 2011 of 37,816; it is also the largest town by area, at 25.19 sq km (9.73 sq mi).
In 2003 Dundalk was amongst nine cities and towns to be designated Gateway status in the Irish Government's National Spatial Strategy.
The Dundalk area has been inhabited since at least 3500 BC, in the Neolithic period. A tangible reminder of their presence can still be seen in the form of the Proleek Dolmen, the eroded remains of a megalithic tomb located at Ballymascanlon two miles to the north of Dundalk. Celtic culture arrived in Ireland around 500 BC. According to the legendary historical accounts, the group settled in North Louth were known as the Conaille Muirtheimne and took their name from Conaill Carnagh, legendary chief of the Red Branch Knights of Ulster. Their land now forms upper and lower Dundalk.
Dundalk had been originally developed as an unwalled (meaning village; translates literally as "Street Townland"). The streets passed along a gravel ridge which runs from the present day Bridge Street in the North, through Church Street to Clanbrassil Street to Earl Street, and finally to Dublin Street.
In 1169 the Normans arrived in Ireland and set about conquering large areas. By 1185 a Norman nobleman named Bertram de Verdun erected a manor house at Castletown Mount and subsequently obtained the town's charter in 1189. Another Norman family, the De Courcys, led by John de Courcy, settled in the Seatown area of Dundalk, the "Nova Villa de Dundalke". Both families assisted in the fortification of the town, building walls and other fortification in the style of a Norman fortress. The town of Dundalk was developed as it lay close to an easy bridging point over the Castletown River and as a frontier town, the northern limit of The Pale. In 1236 Bertram's granddaughter, Rohesia commissioned Castle Roche to fortify the region, and to offer protection from the Irish territory of Ulster.
The town was sacked in 1315, during the Bruce campaign. After taking possession of the town Edward Bruce proclaimed himself King of Ireland and remained here for nearly a whole year before his army was totally defeated and himself slain after being attacked by John de Birmingham.
The modern town of Dundalk largely owes its form to Lord Limerick (James Hamilton, later 1st Earl of Clanbrassil) in the 17th century. He commissioned the construction of streets leading to the town centre; his ideas came from many visits to Europe. In addition to the demolition of the old walls and castles, he had new roads laid out eastwards of the principal streets. The most important of these new roads connected a newly laid down Market Square, which still survives, with a linen and cambric factory at its eastern end, adjacent to what was once an army cavalry and artillery barracks (now Aiken Barracks).
In the 19th century the town grew in importance and many industries were set up in the local area. This development was helped considerably by the opening of railways, the expansion of the docks area or 'Quay' and the setting up of a board of commissioners to run the town.
The partition of Ireland in May 1921 turned Dundalk into a border town and the Dublin–Belfast main line into an international railway. The Irish Free State opened customs and immigration facilities at Dundalk to check goods and passengers crossing the border by train. The Irish Civil War of 1922–23 saw a number of confrontations in Dundalk. The local Fourth Northern Division of the Irish Republican Army under Frank Aiken, who took over Dundalk barracks after the British left, tried to stay neutral but 300 of them were detained by the National Army in August 1922. However, a raid on Dundalk Gaol freed Aiken and over 100 other anti-treaty prisoners; two weeks later he retook Dundalk barracks and captured its garrison before freeing the remaining republican prisoners there. Aiken did not try to hold the town, however, and before withdrawing he called for a truce in a meeting in the centre of Dundalk. The 49 Infantry Battalion and 58 Infantry Battalion of the National Army were based in Dundalk along with No.8 armoured locomotive and two fully armoured cars of their Railway Protection Corps.
For several decades after the end of the Civil War, Dundalk continued to function as a market town, a regional centre, and a centre of administration and manufacturing. Its position close to the border gave it considerable significance during the "Troubles" of Northern Ireland. Many people were sympathetic to the cause of the Provisional Irish Republican Army and Sinn Féin. It was in this period that Dundalk earned the nickname 'El Paso', after the Texan border town of the same name on the border with Mexico.
On 1 September 1973 the 27 Infantry Battalion was established with its Headquarters in Dundalk barracks, renamed Aiken Barracks in 1986 in honour of Frank Aiken.
Dundalk suffered economically when Irish membership of the European Economic Community in the 1970s exposed local manufacturers to foreign competition that they were ill equipped to cope with. The result was the closure of many local factories, resulting in the highest unemployment rate in Leinster, Ireland's richest province. High unemployment produced serious social problems in the town that were only alleviated by the advent of the Celtic Tiger investment boom at the start of the 21st century. Dundalk's economy has developed rapidly since 2000. Today many international companies have factories in Dundalk, from food processing to high-tech computer components. Harp Lager, a beer produced by Diageo, is brewed in the Great Northern Brewery, Dundalk.
The Earls of Roden had property interests in Dundalk for over three centuries, and at an auction in July 2006 the 10th Earl sold his freehold of the town, including ground rents, mineral rights, manorial rights, the reversion of leases and the freehold of highways, common land, and the fair green. Included in the sale were many documents, such as a large 18th century estate map. The buyer was undisclosed.