The remains of the Castle of Lonmay are found near Netherton of Lonmay, to the north of Loch Strathbeg in Buchan, Scotland. The remains are not located in the modern village of Lonmay which is approximately 6km to the south west. It was described by W. Douglas Simpson as one of the nine castles of the Knuckle, referring to the rocky headland of north-east Aberdeenshire.
The castle "may have been a motte". It has long ceased to be in existence and there are very few remains to be found, all of which are buried under constantly shifting sand dunes that have over time engulfed the site.
The castle provided protection to the north-shore of the estuary that used to flow into Strathbeg Bay, before it closed off forming Loch Strathbeg around 1720. The south-shore (with Starny Keppie harbour and the village of Rattray) was protected by the Castle of Rattray.
The remains are found "in the Links".. "near the sea" however "all the stones have been carried off, and employed in building farm-houses" and so "except the name, all tradition respecting this building is lost".
- Simpson, W.D. (1949). "Cairnbulg Castle, Aberdeenshire" (PDF). Proceedings of the Society of Antiquaries of Scotland. 83: 32–44.
- "Castle Hill, Rattray". Archived from the original on 2007-09-27. Retrieved 2007-06-11.
- "Castle of Lonmay". Retrieved 2007-08-06.
- "An introduction to the Royal Burgh of Rattray". Archived from the original on 2007-05-17. Retrieved 2007-06-13.
- "Society for the Benefit of the Sons and Daughters of the Clergy" (1845). "The New Statistical Account of Scotland". Retrieved 2007-08-13.
- The Castle is not normally included on modern maps (Ordnance Survey grid-reference: ), but this 1931 OS map of the area shows the remains of Lonmay Castle to the north of Loch Strathbeg as "Site of Castle".
- Images of the immediate local area (though not the castle site) from the Geograph project.