Carlow (originally Catherlogh). I. A S. E. county of Ireland, in the province of Leinster, bounded by the counties Wicklow, Wexford, Kilkenny, and Queen's; area, 346 sq. m.; pop. in 1871, 51,472. It is level except on the south, where the Blackstairs and Mt. Leinster ranges give a rugged character to the district. The rivers are the Slaney and the Barrow. The county is of granite formation, covered in the plains by beds of gravel, and cropping out in the eminences of Mt. Leinster and the Black-stairs. It is well known for its agricultural character and produce. Out of the whole area of the county there are but 23,000 acres uncultivated, and cereals, roots, and green crops grow luxuriantly. It is one of the principal dairy counties of Ireland. The history of the county is, from its central position, closely connected with that of the English conquest and the Irish struggles to recover their independence. In 1798 Carlow was the seat of important movements. The antiquities are the cromlechs and the cathedral at Old Leighlin, a castle of the Butlers at Clonmore in fine preservation, and several other remains in various parts of the county.

The chief towns are Carlow, Tullow, and Bagnalstown. II. A parliamentary borough, town, parish, and capital of the county, at the confluence of the Burren with the Barrow, 44 m. S. W. of Dublin; pop. of the borough in 1871, 7,773. The principal edifices are a fine court house, a jail, a parish church, a Roman Catholic cathedral and college, two nunneries, a lunatic asylum, infirmary, hospital, workhouse, barracks, and two bridges. There are several diocesan and national schools.. The population are largely engaged in the provision trade. There are several flour mills and malt houses, and it is an important market for agricultural produce. The castle, of which the remains are still extant, built in the 12th century, was the nucleus of the town, which was made a borough in 1208.