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. It is about 58 km (36 mi) west of Galway city, at the far western end of Galway Bay, Lettermullen is the westernmost of three islands; Lettermullen, Gorumna and Lettermore, along with smaller islands collectively known as Ceantar na nOileán ("District of the Islands") connected to the mainland by the bridges and causeways of R374.

Lettermullen is in the parish of Kilcummin, barony of Moycullen, and province of Connaught. It forms one side of Kiegall Bay, and its northern end is part of the shore of Casheen Bay. The island comprises about 100 hectares (250 acres) of arable and pasture land. The inhabitants are chiefly employed in herring and cod fisheries and in the collection of seaweed for manure. Lettermullen is connected to the islands of Dinish, Furnish, Inisherk and An Crappagh.

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.

Lettermullen is part of the Gaeltacht (Irish-speaking region of Ireland) and Irish is the most common spoken language. Accordingly, its official name is Leitir Mealláin.

A very well preserved Signal Station is situated near Golam Head. These stations were built all along the Irish coast by the British from 1804 to 1806 to monitor for maritime invasions.

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

Historical population

Year Pop. ±% 1841 587 —     1851 383 −34.8% 1861 433 +13.1% 1871 497 +14.8% 1881 626 +26.0% 1891 549 −12.3% 1901 533 −2.9% 1911 460 −13.7% 1926 346 −24.8%	Year Pop. ±% 1936 335 −3.2% 1946 329 −1.8% 1951 320 −2.7% 1956 315 −1.6% 1961 280 −11.1% 1966 245 −12.5% 1971 221 −9.8% 1979 216 −2.3% 1981 218 +0.9%	Year Pop. ±% 1986 211 −3.2% 1991 196 −7.1% 1996 204 +4.1% 2002 219 +7.4% 2006 213 −2.7% 2011 241 +13.1% 2016 204 −15.4% 2022 214 +4.9%
Source: Central Statistics Office. "CNA17: Population by Off Shore Island, Sex and Year". CSO.ie. Retrieved 12 October 2016.

• Antoine Ó Flatharta (playwright and scriptwriter)