Without going off into all the cross references and tangents on this BODY of song, and sticking just to the songs with a J(OHNNY) coming down", here's an attempt at a chronology of references. Some has been posted already, but just to get the ducks in a row...

1863        Fedric, Francis. _Slave Life in Virginia and Kentucky_. London: Wertheim, Macintosh, and Hunt.

Frederick (Fedric), an escaped slave, lived circa 1805-1882. Refers to a corn-shucking circa 1820s-1833 on a Virginia or Kentucky plantation.


In the autumn, about the 1st of November, the slaves commence gathering the Indian-corn, pulling it off the stalk, and throwing it into heaps. Then it is carted home, and thrown into heaps sixty or seventy yards long, seven or eight feet high, and about six or seven feet wide. Some of the masters make their slaves shuck the corn. All the slaves stand on one side of the heap, and throw the ears over, which are then cribbed. This is the time when the whole country far and wide resounds with the corn-songs. When they commence shucking the corn, the master will say, "Ain't you going to sing any to-night?" The slaves say, "Yers, Sir." One slave will begin:--

"Fare you well, Miss Lucy. 
                        
ALL. John come down de hollow."


***

1850        Bryant, William Cullen. _Letters of a Traveller_. London: Richard Bentley.

Refers to a corn-shucking bee on a South Carolina plantation in March 1843.

The light-wood-fire was made, and the negroes dropped in from the neighboring plantations, singing as they came. The driver of the plantation, a colored man, brought out baskets of corn in the husk, and piled it in a heap; and the negroes began to strip the husks from the ears, singing with great glee as they worked, keeping time to the music, and now and then throwing in a joke and an extravagant burst of laughter. The songs were generally of a comic character; but one of them was set to a singularly wild and plaintive air, which some of our musicians would do well to reduce to notation. These are the words:

Johnny come down de hollow.
             Oh hollow!
Johnny come down de hollow.
             Oh hollow !
De nigger-trader got me.
             Oh hollow!
De speculator bought me.
             Oh hollow !
I'm sold for silver dollars,
             Oh hollow !
Boys, go catch the pony.
             Oh hollow!
Bring him round the corner.
             Oh hollow!
I'm goln' away to Georgia.
             Oh hollow!
Boys, good-by forever!
             Oh hollow!


***

1856        Olmsted, Frederick Law. _A Journey in the Seaboard Slave States_. New York: Dix and Edwards.

It is 1853 and Olmsted is traveling on a steamboat on the Red River to Shrevport, LA. Though Olmsted observed and mentioned chanties earlier in his career, he make no comparison or recognition here.


" John come down in de holler,
   Oh, work and talk and holler,
   Oh, John, come down in de holler,
Ime gwine away to-morrow.
Oh, John, &c.
Ime gwine away to marry,
Oh, John, &c.

Get my cloves in order,
Oh. John, &c.
I'se gwine away to-morrow,
Oh, John, &c.
Oh, work and talk and holler,
Oh, John, &c.
Massa guv me dollar,
Oh, John, &c.
Don't cry yer eyes out, honey,
Oh, John, &c.
I'm gwine to get some money,
Oh, John, &c.
But I'll come back to-morrow,
Oh, John, &c.
So work and talk and holler,
Oh, John, &c.
Work all day and Sunday,
Oh, John, &c.
Massa get de money,
Oh, John, &c.

After the conclusion of this song, and after the negroes had left the bows, and were coming aft along the guards, we passed two or three colored nurses, walking with children on the river bank; as we did so the singers jumped on some cotton bales, bowed very low to them, took off their hats, and swung and waved them, and renewed their song:

God bless you all, dah ! ladies !
Oh, John come down in de holler,
Farwell, de Lord be wid you, honey,
            Oh, John, come down, &c.
Done cry yerself to def,
            Oh, John. &c.
I'm gwine down to New Orleans,
            Oh, John. &c
I'll come back, dough, bime-by,
            Oh, John, &c,
So far-you-well, my honey,
            Oh, John, &c.
Far-you-well, all you dah, shore,
            Oh, John, &c.
And save your cotton for de Dalmo!
Oh, John, &c

These references suggest quite strongly that the song (or the phrase that was the basis for later songs) was a part of African-American folk-song, predating and/or distinct from both popular minstrel song and modern chanties.