Carlow, or Catherlough, a county of Ireland, in Leinster, 28 miles long and 8 broad, bounded E by Wicklow and Wexford, W by Queen's county and Kilkenny, and N by Kildare, divided into 50 parishes, and sends 3 members to parliament. Chief rivers, the Barrow and Slaney. Pop. 81,287.
[From The New London Gazetteer (1826)]
The Ireland Genealogy Project's County Carlow page, and its listing of the Project's available Carlow Records
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 Carlow 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 Carlow coverage includes Baptismal/Birth Records, Marriage Records, and Griffith's Valuation (Free Access).