If I may be allowed to provide a few observations that would help you direct your own search a bit better until a more knowledgeable party comes along. I make these observations as an enthusiastic amateur, and would happily defer to that more knowledgeable party...

Let's assume, by the greying in his beard, he's about 40-50 here, which means that it's about 1900-1910 when the photo was taken. I can't really find an example (with my google-fu) of a military uniform of that period that resembles the exact configuration of that jacket. HOWEVER, it does resemble some used by several military academies (including military institutes not run by the federal government). Here's an example of what I'm talking about. That's from 1890, but similar-looking, albeit-simplified jackets are still being worn today.

Given that small clue, here's an interesting photograph I just found, from about 1898 (it says at the bottom), and four guys are wearing that sort of jacket.

Given that his epaulets (or whatever that shoulder device is called) resemble those of the US Army, I don't think it'd be an unreasonable working assumption to make that he was in the army about 1890-ish, which seems to fit with the rather, ahem, distressed condition of the uniform.

The buttons are a bit of a wild card, though.