The village name may derive from the terms 'tref' and 'mil' signifying the 'farm of the lesser celandine', a plant which might be expected to grow in the stream which flows through the place, the Nant Trefil.

At 409 metres (1,342 ft) above sea level, the Ordnance Survey recognise Trefil as the highest village in Wales.

The former Brinore Tramroad connected the quarries at Trefil with the Monmouthshire and Brecon Canal at Talybont in the Usk Valley to the north.

Trefil Quarries and Trefil Ddu are noted birdwatching sites; this area is the last remaining site in Gwent where ring ouzel occurs regularly, and other species present include raven, wheatear, stonechat, whinchat, snipe and red grouse.

[7] The village is the site of Trefile Rugby Welfare Club who play in WRU Division 3C East.