Clermont Carn, Mountain summit in County Louth, Ireland.

Clermont Carn is a 510-metre summit in the Cooley Mountains of County Louth, near the border with Northern Ireland. Its top holds a Neolithic court cairn 21 m in diameter and over 4 m high, with three lintels still in place and a corbelled rear. A 120-metre cable-stayed transmission mast stands beside it.

The summit cairn is a Clyde-Carlingford court cairn built in the early Neolithic, c. 4000–3500 BC. It measures 21 m across and over 4 m high, with a 5.5 × 7 m court and a gallery of at least two chambers; three lintels remain and the rear is corbelled. Quarrying and blasting have disturbed the protected National Monument in recent decades.

The Irish name Carnán Mhaighréid Náir means 'cairn of noble Margaret', while 'Clermont' comes from Lord Clermont of Ravensdale. The 'carn' element refers to the burial cairn on the summit, known as Black Mountain Chambered Cairn or Ravensdale Park Cairn.

The summit lies under two kilometres from the Northern Ireland border, and the 120-metre cable-stayed mast of 2002 dominates the top, so expect an exposed, working transmission site rather than a quiet viewpoint. The original self-supporting tower remains, truncated, for microwave links and a 2M amateur radio repeater installed in 1982.

Clermont Carn is the only main television transmitter in Ireland that is vertically polarised, and it feeds no relay transmitters. Its 120-metre cable-stayed mast, erected in 2002, carries Saorview digital television, and the signal reaches Belfast and beyond. Analogue transmissions ceased on 24 October 2012.