Llanelieu (English Llaneleu) is a small settlement and former civil parish (community) in Powys, Wales on the northern edge of the Black Mountains within the Brecon Beacons National Park.

The church of St Ellyw dates from the 13th century and, unusually, escaped Victorian modernization so that it preserves many of its medieval features.

[6] In 1845, Samuel Lewis' topographical entry for Llanelieu noted that "there were formerly several ancient mansions, but they have been all abandoned as family residences by their proprietors, and are at present occupied as farm-houses".

[10] As such, it included a substantial upland area of the Black Mountains, principally along the valley of the Grwyne Fawr where a reservoir was completed between 1908 and 1928.

[11] Lewis in 1845 described the "surrounding scenery as bold, and in some parts romantic",[7] whereas the 1868 National Gazetteer dismissed it as "somewhat of a gloomy cast".