Lettermullen, (Irish: Leitir Mealláin, meaning 'Mealláin's rough hillside' or possibly "the hill with the mill"), is a small island and village on the coast of southern Connemara in County Galway, Ireland.

The northern third of Lettermullan is composed of the same intrusive Devonian-aged granite underlying most of Galway that formed from crustal melting as a result of the Caledonian Orogeny in the late Silurian.

The remainder of the island is made up of Ordovician-aged bedrock of sedimentary marine rocks and basalt.

[3] Lettermullen is part of the Gaeltacht (Irish-speaking region of Ireland) and Irish is the most common spoken language.

A picturesque cemetery is situated just south of R374 immediately after you cross the bridge from Gorumna to Lettermullen.