Caerphilly is a town and community in Wales. It is situated at the southern end of the Rhymney Valley. It is 7 miles north of Cardiff and 9.5 mileā¦Caerphilly is a town and community in Wales. It is situated at the southern end of the Rhymney Valley. It is 7 miles north of Cardiff and 9.5 miles west of Newport. It is the largest town in Caerphilly County Borough, and lies within the historic borders of Glamorgan, on the border with Monmouthshire. At the 2011 Census, the town had a population of 41,402 while the wider Caerphilly local authority area had a population of 178,806.