Entry in progress—B.P.
 
(Oxford English Dictionary)
mudhead, n.
U.S. colloq. (derogatory). A native of Tennessee. Now rare.
1838   T. C. Haliburton Clockmaker 2nd Ser. xix. 289   There’s the hoosiers of Indiana,..the mudheads of Tenessee [etc.].
1847   J. K. Paulding & W. I. Paulding Madmen All ii. ii, in Amer. Comedies 192   Waal, we’ve got some o’ most all kinds: Pukes, Wolverines, Snags, Hoosiers, Griddle-greasers, Buck-eyes, Corncrackers, Pot-soppers, Hard-heads, Hawk-eyes, Rackensacks, Linsey-woolseys, Red-horses, Mud-heads, Green-horns [etc.].
1949   Amer. Speech 24 27   Buckshine, Mudhead, or Whelp for a Tennessean.
 
Google Books
The Clockmaker; or The Sayings and Doings of Samuel Slick, of Slickville
By Thomas Chandler Haliburton
London: Richard Bentley
1838
Pg. 289:
These last have all nicknames. There’s the hoosiers of Indiana, the suckers of Illinoy, the pukes of Missuri, the buckeys of Ohio, the red horses of Kentucky, the mud-heads of Tenessee, the wolverines of Michigan, the eels of New England, and the corn-crackers of Virginia.
 
Google Books
Life in the New World,
Or, Sketches of American Society
By Charles Seatsfield
New York, NY: J. WInchester
1844
Pg. 55:
They would begin the struggle rather to-day than to-morrow; the Hooskiers from Indiana, the Suckers from Illinois, the Pukes from Missouri, the Red-horses from Kentucky, the Buckeyes from Ohio, the Wolverines from Michigan, the Eels from New England, the Mudheads from Gennessee, the Corncrackers from Virginia, they are all ready.
 
Google Books
U. S.
An Index to the United States of America
Compiled by Malcolm Townsend
Boston, MA: D. Lothrop Company
1890
Pg. 81:
NICKNAMES APPLIED TO THE PEOPLE OF THE STATES.
(...)
Tennessee…Mud-head...“A nickname applied to natives of Tennessee.”—Bartlett. (No reason given.)