Trefil is a small village north of Tredegar. It lies at the top of the Sirhowy valley and is only one mile from the Brecon Beacons National Park. It is believed that the village's name means “farm of the lesser celandine”, a plant which sometimes grows in the Nant Trefil, a small stream which flows through the village.
The village is bordered to the south by Tredegar, to the north by the Crawnon valley, to the west by the Trefil Ddu moorlands and to the east by Rassau. Nearby towns and villages include Ebbw Vale, Tredegar, Rhymney, Merthyr Tydfil, Pontsticill, Llangynidr, Rassau, Beaufort, Abergavenny, Crickhowell and Llangattock.