Ler: the Irish sea-god
Lethglas: Dun Lethglaisse, now Downpatrick, in Ulster
Lettre Luasce: between Cualnge and Conalle
Lia Mor: in Conalle Murthemni
Liath Mache: 'the Roan,' one of Cuchulain's two horses.
Lia Ualann: in Cualnge
Linè (or Mag Linè): Moylinne, in the County Antrim
Loch Ce: Lough Key, in the County Roscommon
Loch Echtrann: Muckno Lake, south of Sliab Fuait, in the County Monaghan
Loch Erne: Lough Erne, in the County Fermanagh