The name "Loch Earn" is thought to mean "Loch of Ireland", and it has been suggested that this might derive from the time when the Gaels were expanding their kingdom of Dalriada eastwards into Pictland.
It is a long narrow loch, 17 km west of Crieff and is approximately 10.5 km long, 1.2 km at its widest point (56.38N, 4.22W) and at its deepest point (approximately half way along) about 87 m. Lochearnhead village is situated at the western end of the loch and St. Fillans village at the eastern end. From here, the River Earn flows eastwards from the loch, through Strathearn, and eventually joins the Firth of Tay some 75 km away. Lochearnhead is the centre for the water sports activities on the loch; water skiing, canoeing and sailing. The loch is also stocked regularly with brown and rainbow trout and fishing, by permit, is possible from the shore and by boat.
Loch Earn is unusual due to a tidal like effect, "seiching" ,caused by wind along its length and by thermal stratification and is the only Scottish Loch to be so affected. Loch Geneva is probably the best known loch with similar "tides".
One of Loch's crannogs lies just offshore from Edinample castle, but probably of greater interest is the small island, almost certainly a crannog, at the eastern end which was occupied by the Clan Neish until they were decimated by a raid in the night by the Clan MacNab. Even this incident proved the defensive nature of the crannog since the MacNabs had to carry a boat over the hills from Killin in order th surprise the clan Neish.