Ian's list is pretty good, but there are errors.
Under USA Regional, the Frank C. Brown Collection of North Carolina Folklore definitely was published, in 7 volumes by the Duke University Press. Especially important are vol. 2, Folk Ballads from North Carolina, vol. 3, Folk Songs from North Carolina, vol. 4, The Music of the Ballads, and vol. 5, The Music of the Folk Songs. Volumes 4 and 5 are obtainable for a reasonable price (ca. $30 each) but 2 and 3, hopefully, will be in your town library. A complete set was advertised recently for $1300. I don't know where Ian got the nonsense about "T for Texas...." (not in his "The Music of the Folk Songs," not a folk song, certainly not in Randolph).
The Vance Randolph 4-volume set, Ozark Folksongs, has been reprinted and is available through bookdealers for less than $150.
Vance Randolph was not self-taught; he held degrees from Kansas State and Clark Universities, was in graduate school at the University of Kansas seeking a Ph. D. in psychology but his other interests intervened. Associates in preparing his material included Profs. Kittredge of Harvard and Belden of Missouri (an English professor who also edited two volumes of the Brown Collection). Randolph contributed to folklore journals. Very few American academics who collected folk songs ever had a degree specializing in folklore or music; they were "self-taught."
The very useful "Songs of the American West" by Lingenfelter, Dwyer and Cohen is not on the Regional list.
Botkin's easily obtained regional books are not listed.
Carl Sandburg's "The New American Songbook," the supplement to "The American Songbag," is not in the USA general listing.