It is located in the province of Leinster at the meeting of N78 and R694 roads about roads north of Kilkenny city in the southeast of the island of Ireland. Castlecomer rural area has an area of 23,417 hectares. The town square has Georgian houses surrounded by Lime trees.
As of the 2006 census, by the Central Statistics Office, Castlecomer town's population, which includes Donaguile, was 1,531. This was a 3.3% change since 2002. The Castlecomer rural area has a population of 8,280.
Castlecomer railway station opened on 21 February 1921 but closed for passenger traffic on 26 January 1931 and closed altogether on 1 January 1963. Castlecomer is on the Dublin to Clonmel Bus Eireann bus route.
The local government is Kilkenny County Council. Castlecomer and its rural area forms an Electoral District which includes Attanagh, Ballyragget, Castlecomer, Clogh, Clogharinka, Moneenroe, Mothell and Muckalee.
Agriculture employs 100 people. The Castlecomer district has 60 farms. These range between 10 and 100 hectares with a total of 2003 hectares being farmed. There are 4451 cattle and 768 sheep, and farming is done with grassland machines, tillage machines, tractors, winter feeding and milking equipment. Specialist farms include beef production, dairy and mixed grazing linestock.
Deen Celtic A.F.C. is the local Soccer Club in Castlecomer.