You are probably thinking of one of two pieces that more properly belong in the classical music categary than the folk category, although both show significant folk influence in the composition and have often been performed by people who are sometimes thought of as folk-singers.

The first is "Freedom Train" by Earl Robinson. The only recording that seems to now be in print is by Paul Robeson, but who could ask for a better performer? Earl Robinson composed quite a few well-known songs that people think of as folksongs, including "Joe Hill," and "Black and White" (The ink is black/The page is white/Together we learn to read and write/To read and write . . .) Many of his compositions became well-known when sung by Paul Robeson, particularly the "Ballad for Americans," which is more like a folk-cantata than a folk-song, but which is sometimes sung by gatherings of "folksingers."

The second is "Lincoln Portrait" by Aaron Copland, composed for a symphony orchestra with a narrator. There are several recordings in print. Copland was an associate of Charles Seeger, Ruth Crawford, Carl Sandburg and the Lomaxes. The influence of folk music, and particularly field recordings by the Lomaxes and others for the Library of Congress, upon his compostions is well-known. His works have been so successful that it seems likely that more of us first learned such traditional tunes as "Simple Gifts" and "Bonaparte's Retreat" from hearing his compositions rather than from traditional sources.

The "folk music" wheel keeps turning. Here I think you want the part of the classical music world that shows its influence.