Carlow, a small inland county of Leinster, Ireland, with an area of 346 sq. m. Except for Mount Leinster (2610 feet), on the south-east border, it is a triangular fertile level, or gently undulating plain, between the Wicklow and Wexford range of hills on the east, and the highlands beyond the Barrow on the west. The chief rivers are the Barrow and Slaney. On the west side of the county begins the great coal district of Leinster. Barely one-third of the entire area is under oats, wheat, potatoes, and other crops. There are many dairies on the plains. Along the Barrow, which falls more than a foot per mile, are many large corn-mills. Pop. (1841) 86,228; (1871) 51,472; (1901) 37,748, of whom 36,139 were Catholics. Since 1885 the county has returned but one member to parliament. The chief towns are Carlow, Bagenals-town, and Tullow.
Carlow, the county town, stands at the influx of the Burren to the Barrow, 56 miles SW. of Dublin by rail. It has a Catholic cathedral, remains of De Lacy's castle (1180), the county court-house, extensive flour-mills, and is the emporium for the agricultural produce of the district. Till 1885 it returned a member. Pop. (1851) 9121; (1901) 6513.