1950s; earliest use found in Wilfred Granville (fl. 1952–1962). Humorous blend of mummer and Somersetshire, alternative name (now rare or historical) for the county of Somerset; compare shire.
Definition of Mummersetshire in US English:
Mummersetshire
noun
Mummerset.
Origin
1950s; earliest use found in Wilfred Granville (fl. 1952–1962). Humorous blend of mummer and Somersetshire, alternative name (now rare or historical) for the county of Somerset; compare shire.