"Onich, a village in Kilmallie parish, Inverness-shire, at the northern side of the entrance to Loch Leven, 2½ miles WNW of Ballachulish ferry. It has a post office and a public school. Slate quarrying was begun here on the Lochiel estate in 1872."
Extract from Groome's Ordnance Gazetteer of Scotland, c. 1895
It has been observed that in the 1911 Census of Scotland there is possible incorrect indexing of the 1911 Census data.
(Glencoe &) Ballachulish in Duror QSP in 'Lismore & Appin Parish' (525) is in Argyll however you will need to search for it in Inverness-shire as Ballachulish.
Ballachulish in the Inverness-shire part of 'Ballachulish & Corran of Ardgour' QSP (506) is indexed under Inverness-shire as Ballachulish.
The Ballachulish area (Ballachulish, Ballachulish & Corran of Ardgour, Lismore & Appin, Onich & Ballachulish) can perhaps be described as one of Argyll's peculiarities. Historically, the name Ballachulish is proper to the area on the North side of Loch Leven now known as North Ballachulish. However the name was later appropriated to describe the slate quarries developed at East Laroch on the South side of Loch Leven, and eventually adopted for the whole of the former Laroch village. See Wikipedia - Ballachulish.
This has implications for those searching for not only the physical presence of their ancestors, but also those searching for relevant records. See the note under Census above.
You can see maps centred on OS grid reference NN025615 (Lat/Lon: 56.703383, -5.227771), Onich which are provided by: