As so often, sam, we’re talking past one another because you’re looking for the absolute first use and I’m looking at when the use became popularly used.
An ngrams search from 1870-1905 shows what I mean. Hobo has almost no uses before 1905. Almost no is not the same as none, and that article is surely a fascinating find. From its tone, hobo is so established you may have to go back many years for a first use.
For people not familiar with the Google Books database: don’t bother clicking on that 1870-1871 link and expect to find an early use of hobo. Periodicals are dated by the first issue in the run, so the first link takes you to a magazine article from 1896. The second link is in Swahili. And so forth.