@boomerang,
Well, I've got about 600 Dixieland jazz cd's ...
According to the most common explanation of the name 'Dixie-(land)', $10 notes issued before 1860 by the Citizens’ Bank of New Orleans and used largely by French-speaking residents were imprinted with dix (French: “ten”) on the reverse side; hence the land of Dixies, or Dixie Land, which applied to Louisiana and eventually the whole South.
(References to the "Mason-Dixon-Line" are another reason, according to some sources.)
Dixieland as a jazz style is often ascribed to the jazz pioneers in/from New Orleans, but also descriptive of styles honed by slightly later Chicago-area musicians.
The term also refers to the traditional jazz that underwent a popular revival during the 1940s and 1950's (especially in the UK, but other European countries as well) and that continued to be played into the 21st century.
The name seems to have appeared for the first as name of a group, in 1916, the "Original Dixieland Jass Band" [with two 's'!].