The county supposedly takes its name from Lugh, the (little) Celtic sun-god and god of light, in common with Leiden, Lyons, Lugano and, possibly, London. The County Council uses the Irish form 'Lughaí' which is closer to the traditional form than the standard 'Lú'.

Lugh was said to be the divine father of Cú Chulainn and the county also has the strongest claim to be both his homeland and the place of his death, as part of the Táin Bó Cuailgne, or the Cattle Raid of Cooley, after which both a waymarked footpath and a long-distance cycle touring route are named.