The estate is large and sprawling, built in the mid-1980s as temporary housing during the redevelopment of Pillgwenlly (Pill Newport). The residents liked the houses and never left. It is built around the original Thornhill farm house, which is still situated in the middle of the estate. The farm originally farmed pigs, and the woodland now surrounding the main estate has remains of the old walls and pig sties. The estate is divided into small cul de sacs that are named after Welsh rivers or lakes. The main thoroughfare is Hafren Road (Hafren is Welsh for the River Severn).
At the centre of the estate is a small shopping precinct which is home to a convenience store, newsagent, fish and chip shop, chemist, and pub.
Thornhill is the most economically-improved area of Cwmbran and in the wider Torfaen area.