Old Castle Lachlan was built in the 13th century though much of the ruins today date from the 15th century. It was the stronghold of Clan MacLachlan until 1746 when it was attacked by a British Government warship. Though little damage was done, its occupants fled, and it was never again occupied. New Lachlan Castle was built as a replacement in 1790, around 1 kilometer to the north-east.
Old Lachlan Castle is on the bank of Loch Fyne, a sea loch on the west coast of Argyll and Bute, Scotland.