Erraid (Scottish Gaelic: Eilean Earraid) is a tidal island approximately one mile (two kilometres) square located in the Inner Hebrides of Scotland.

The island receives about 1,000 millimetres (40 in) of rain[6] and 1,350 hours of sunshine annually, making it one of the driest and sunniest places on the western seaboard of Scotland.

[12][13] Davie Balfour is trapped on the island by his ignorance, and as he says in Kidnapped: Chapter XIV- A sea-bred boy would not have stayed a day on Earraid; which is only what they call a tidal islet, and except in the bottom of the neaps, can be entered and left twice in every twenty-four hours, either dry-shod, or at the most by wading.

And even as it was, I had paid for it pretty dear, not only in past sufferings, but in my present case; being clothed like a beggar-man, scarce able to walk, and in great pain of my sore throat.

Stevenson also includes a description of the island: It was still the roughest kind of walking; indeed the whole, not only of Earraid, but of the neighbouring part of Mull (which they call the Ross) is nothing but a jumble of granite rocks with heather in among.