Washington University has several St. Louis city directories, dating from 1821 to 1877, online and I searched several of those looking for information about Hollenback. I had previously found information about him in the 1860 city directory and wanted to confirm that using other directories. I was not only able to do that but was also able to find some additional biographical information about the illusive Hollenback.
In the 1857 directory, I found this entry:
Hollenbeck, J.M., cl'k. 3 olive; r. 109 n. 3d.
Hollenbach, Joseph, clerk, bds. 109 n. 3d
Hollenbeck, Joseph M., clerk, Scott & Covert, bds. 109n. 3d.
Hollenback Joseph, constable, bds. 109 N. 3d.
The directories contain other pieces of information that are new. First, Hollenbach's middle initial is "M." This is rather important because it's always been difficult, given all of the different spellings of his last name (which is evident in the 1859 directory), to identify Hollenback in databases. A middle initial will help identify him in the future. The other piece of new information is that Hollenback worked as a clerk for Scott & Covert, who are listed in the directory as "landagents" and had offices on Third Street. Given the evidence, I believe he was working for Scott & Covert as early as 1857. The interesting question here is when and how Hollenback became a constable. I don't have an answer for that but it certainly happened sometime in the later part of 1859 or early in 1860.
Sadly, the directories do not give us any clues on what happened to Hollenback. My best guess is that he joined the Missouri Militia in 1864 and died in 1866. Hollenback is not listed in the city directories in 1864, 1865 or 1866 and that kind of (sort of) supports my guess but all it really tells us is that he wasn't living in St. Louis at the time. The other, most likely, option about the fate of Hollenback is that he died of typhoid fever in October of 1860. The reason I like that possibility is that I see no record of Hollenback being involved with the Empire Club after July of 1860. There is no contemporary record of his involvement with the club during the war years and certainly nothing after the war. I have no doubt that he died young - either in 1860 or 1866.
But the bottom line is that we know more about Joseph Hollenback today then we did yesterday and that's a good thing, especially when you consider that the list of things we can prove about Hollenback is rather short.