Louth (louħ) [key], county (1991 pop. 90,724), 317 sq mi (821 sq km), NE Republic of Ireland. The county seat is Dundalk. The region borders the Irish Sea from the mouth of the Boyne River to Carlingford Lough. The terrain is an undulating plain, except for a hilly district in the north. Principal rivers are the Fane, the Glyde, and the Dee. Among the industries are cotton and linen manufacturing, brewing, and food processing. Dundalk, Drogheda, and Greenore are ports. The region is associated with the exploits of the legendary Irish hero Cuchulain and was, near Annagassan on the Glyde, the site of a major Viking fort and settlement (est. A.D. 841) that was later eclipsed by Dublin.