Castle Lachlan lies on the eastern shore of Loch Fyne, near Newton. According to the Clan Maclachlan Society website, the original castle dates back to the 13th century. The original castle was later replaced in the 15th century with the keep or tower that today is in ruins. The ruinous castle lies about 70 feet (21.3 m) north to south, 54 feet (16.5 m) east to west, and at its highest point 43 feet (13.1 m) feet high.
The new Castle Lachlan which stands about a ten minute walk away from the ruinous old Castle Lachlan, is the seat of Clan Maclachlan. It was first built in the late 18th century, with the construction overseen by Donald Maclachlan. The new house was first built in the Queen Anne Style, then later at the end of the 19th century the "castle" was transformed into the Scottish baronial house that stands today. The castle, upon the 1,500 acres (2.3 sq mi; 6.1 km2) estate, has been divided in two with the chief residing in one part and the second available for rent.