If you look above you'll see that the best guess as to the origin of "I've Been Working on the Railroad" is that it was published as "Levee Song" in the 1894 edition of Carmina Princetonia - although portions of the song came earlier. Masato posted the 1894 lyrics in this thread. Take a look at the crosslinked threads listed at the top of this page.
I guess you could say this is three songs linked together: "I've Been Working on the Railroad," "Someone's In the Kitchen With Dinah," and "Dinah Won't You Blow Your Horn." Another interesting aspect of the song is that it's a relatively complex song, and yet everybody seems to know it with exactly the same lyrics and melody. I wonder when and how it achieved such universality.

-Joe-