Dundalk ("Dealgan's fort") is the county town (the administrative centre) of the county of Louth in Ireland. The town is on the Castletown River, which flows into Dundalk Bay on the east coast of Ireland. It is near the border with Northern Ireland (which is 7 km from the town centre by road and 3.5 km at the nearest points by air), and is equidistant between Dublin and Belfast (80 km from both). It is the eighth largest urban area in Ireland, with a population of 39,004 as of the 2016 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 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 Cu Chulainn are set in the district and the motto on the town's coat of arms is Me do rug Cu Chulainn croga (Irish) "I gave birth to brave Cu Chulainn".

The town developed brewing, distilling, tobacco, textile, and engineering industries during the nineteenth 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 operations in the aftermath of the Partition of Ireland in 1921 and the accession of Ireland to the European Economic Community in 1973. Following the Celtic Tiger period of the late 20th century, new industries have been established including pharmaceutical, technology, financial services, and specialist foods.

There is one third-level education institute—Dundalk Institute of Technology. The largest theatre in the town, An Táin Arts Centre, is in the Town Hall, and the restored buildings of the nearby former Dundalk Distillery house both the County Museum Dundalk and the Louth County Library. Sporting clubs include Dundalk Football Club (who play at Oriel Park), Dundalk Rugby Club, Dundalk Golf Club, and a number of Gaelic football clubs. Dundalk Stadium is a horse and greyhound racing venue and is Ireland's only all-weather horse racing track.