Trefonen, Treflach and Nantmawr are situated between three to five miles SW of Oswestry in the County of Shropshire.
The villages nestle between the Shropshire Plain and the Welsh Hills and it is considered a prime example of a dramatic landscape marking the transition from lowland to upland. The highest point is a hill above Trefonen at 341 metres, and the lowest point is at 135 metres in Nantmawr. The difference causes the roads and lanes to be steep and twisting, but it also contributes to the many spectacular views in and out of the settlements.
Trefonen lies close under the eastern slope of a ridge running north-south to the west of Oswestry. The nearby summit of Mynydd Myfyr is just over a mile from the village centre from which there are clear views across Trefonen. A little over half the village is sited on the hillside, whereas the remainder is sited to the east of the main road and bounded by open and flatter farmland. This is crossed from west to east by Trefonen Brook forming a significant and important valley for wildlife. An area of mixed woodland, Bwyltai Wood, of further natural and wildlife importance, owned by Shropshire Wildlife Trust, lies on the southern slope of the valley, near to the village.