Surprisingly, Chass McDevitt recorded Freight Train first, even before Libby Cotton herself. There's an enteresting shortstory on this and her life in general at this link: http://www.smithsonianmag.si.edu/smithsonian/issues00/oct00/object_oct00.html
An excerpt: "One afternoon Peggy Seeger heard Cotten singing "Freight Train" and asked to learn it. At the time, Ruth (Peggy's mother) was compiling a collection of children's folk songs and included one by Cotten. Encouraged, Cotten began to put together more new songs and, with the Seegers' help, began occasionally singing and playing in public.

In the mid-1950s, a grown-up Peggy Seeger sang "Freight Train" during a concert tour in England, and the song was soon recorded — without permission or credit — by a British singer (McDevitt). It became a hit in Britain, and the furor over the songwriting credit and royalties helped create a demand for Libba Cotten's music. Her first album, "Negro Folksongs and Tunes," was cut in 1958 on the Folkways label, which the Smithsonian Institution acquired in 1987."