Mummerset

Mummerset was, according to one account but not others, the West Country county of England in which Stockbridge was located. Its local lord, the Earl of Mummerset, sat in Stockbridge Castle. Mummerset was in the West Country. (AUDIO: Castle of Fear)

Behind the scenes
Mummerset isn't real, but it is a "real fiction". A deliberate corruption of "Somerset", it's just shorthand for "anything that generally comes from the West Country". The joke in Castle of Fear is that Hubert isn't just a fraud in himself — he's not the "sixth Earl of Mummerset" — but that there is no Mummerset and therefore no earldom at all.

Of course, the story doesn't actually make this point — it's subtext for the knowledgeable listener — so in the DWU, there is a Mummerset.