Thanks for the link!

But there's one more stanza:

"We learned this song from Tommy Tompkins,
Hi-Oh, the rolling river.
Tompkins of the Fifth cavalree.
Ha, ha. We're bound away
For the wild Missouri.

The 5th Cavalry was organized in 1856 and served during the Civil War. Its postbellum service was in Arizona until 1876 when, after the Battle of the Little Big Horn, it was moved north to assist the 7th.

If the 5th Cavalry reference in the song means anything (and maybe it doesn't), 1876 would seem to be its earliest possible date - at least for that stanza.

"Tommy Tompkins" reappears in the longer version the Lomaxes credit to Major Isaac Spalding Of the office of the Army Chief of Staff, but without the 5th Cavalry.