"Louth, a county of Ireland, bounded S and SW by E. Meath, W by Monaghan and Cavan, N by Armagh, NE by the bay of Carlingford, and E by the Irish channel, 27 m. long, and 18 broad. It is in general rich and well cultivated, and has little waste ground. Chief river, the Boyne. Principal towns, Carlingford, Dundalk, Drogheda, and Colton. The linen manufacture is carried on to a great extent. It sends 1 member to parliament. Pop. 107,070."
[From The New London Gazetteer (1826)]
The Irish Ancestors website (subscription) has the following types of records: State Registration of Births, Marriages & Deaths, Census returns, Land records, Church records, Genealogical Office records, Gravestone inscriptions, Directories, Newspapers, Wills, Deeds, and Occupations.
The Fianna website's pages for County Louth provide important addresses and extensive information about online and other genealogy resources.
Roots Ireland (subscription) "offers access to a unique database of more than 20 million Irish records". Its Louth coverage includes Baptismal/Birth Records, Marriage Records, Burial/Death Records and Griffith's Valuation (Free Access).