The Campbell of Loudoun tartan is also very similar to the Black Watch tartan in terms of sett and colour and it is almost identical to the Campbell of Breadalbane tartan with a white and yellow stripe instead of just yellow stripes. There is a castle named after the branch in Ayrshire, it was built for the 6th Countess of Loudoun in the early 19th Century.
This was the accepted version of Campbell of Loudoun as shown in the 1906 W & A K Johnston books. It differs from the earlier sett in Clans Originaux where there are no black tramlines on the blue. The rarest of the Campbell tartans, Loudoun is nevertheless, acknowledged by the Mac Cailein Mòr, Chief of the Clan Campbell.
In 'Campbell Tartan', written by Alastair Campbell of Airds the younger in 1985, he lists the four approved Campbell tartans: the Campbell (also known as "Ancient Campbell" and "Campbell Ancient" in the marketplace), which is the same as the Black Watch; the Campbell of Cawdor; the Campbell of Beadalbane; and the Campbell of Loudoun. Of the Campbell of Argyll tartan, he writes, “This is not a pattern which has the Chief’s approval as an official Campbell tartan and purchasers should avoid it if they wish to be correct.” To be accurate, the past 7 Clan Campbell Chiefs have disavowed, some very strongly, the so called "Campbell of Argyll" tartan.