John Wesley Work (c. 1872-1925) composed "Go Tell It on the Mountain," 1907, as a solo piece, according to "Hymns and Carols for Christmas," quoting from the website of Prof. Gracia Grindal, Luther Seminary: http://hymnuts.luthersem.edu/hcompany/texts/hymn070.htm.

It may also have been printed in Folksongs of the American Negro, published in soft cover in 1907, hard cover 1915.
Supposedly it is based on "the old Negro spiritual When I Was a Seeker" but this spiritual has not been collected.