Carlow is the second smallest county in Ireland. In the north, the broad valleys of the rivers Barrow and Slaney are famed for their fertility and are intensively farmed. In the south, Mount Leinster and the Blackstairs form a natural imposing border with Wexford.
Before the Norman invasion in the twelfth century, Carlow formed the northernmost part of the Gaelic kingdom of Uí Cinnseallaigh, which also took in parts of the neighbouring counties of Wicklow and Wexford. The county was part of the lands of Dermot MacMurrough, the Leinster king who formed the first alliance with the Normans and facilitated their invasion in the twelfth century. Norman castles still stand at Carlow town, Leighlin and Tullow. In the 1798 rebellion, Carlow was the scene of some of the most bloody fighting.
In the Famine and the subsequent emigration, Carlow was badly affected; its population shrank from 86,000 in 1841 to 41,000 in 1966, a drop of 52%. Today the population stands at around 45,000.
Surnames strongly associated with the county include Brennan, Byrne, Kavanagh, Hayden, Nolan and Scully.