Dundalk (dʌnˈdɔː(l)k ; Dún Dealgan ˌd̪ɣuːn̪ɣ ˈdjalɣɡənɣ), meaning "the fort of Dealgan", is the county town (the administrative centre) of County Louth, Ireland. The town is on the Castletown River, which flows into Dundalk Bay on the east coast of Ireland. It is halfway between Dublin and Belfast, close to the border with Northern Ireland. It is the seventh largest urban area in Ireland, with a population of 43,112 as of the 2022 census.
Having been inhabited since the Neolithic period, Dundalk was established as a Norman stronghold in the 12th century following the Norman invasion of Ireland, and it became the northernmost outpost of The Pale in the Late Middle Ages. The town came to be nicknamed the "Gap of the North" where the northernmost point of the province of Leinster meets the province of Ulster. The modern street layout dates from the early 18th century and owes its form to James Hamilton (later 1st Earl of Clanbrassil). The legends of the mythical warrior hero Cú Chulainn are set in the district, and the motto on the town's coat of arms is Mé do rug Cú Chulainn cróga ("I gave birth to brave Cú Chulainn").
The town developed brewing, distilling, tobacco, textile, and engineering industries during the 19th century. 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. It later suffered from high unemployment and urban decay after these industries closed or scaled back both in the aftermath of the Partition of Ireland in 1921 and following the accession of Ireland to the European Economic Community in 1973. New industries have been established in the early part of the 21st century, including pharmaceutical, technology, financial services, and specialist foods.
There is one third-level education institute—Dundalk Institute of Technology.