the rankings for departments as a whole are worthless, as it's really all about your subfield. And those rankings don't mean a damn thing either, for example US News ranks Harvard pretty high in Latin American history, but they only have one tenured professor, and her focus seems more on the United States than anything else. I imagine having a LA history PhD from Harvard would be impressive for 5 seconds, until adcoms remembered that you basically studied with one historian the whole time (plus itinerants). In addition, I would consider the subfield itself, I have heard it is a bit easier to get hired if one's specialty is something rare, like African history. The odds are still bad, but better than trying to compete in a popular field like Early Modern British History.
OSU is well regarded, I would've been overjoyed to have been accepted there, but instead I'm shipping off to a lesser known institution. I'm pretty happy about that actually, my advisor is very well regarded in his subfield, so much so that all two of his graduates have eventually found themselves tenure track jobs. (that's a 100% placement rate, never mind the small sample size...) You wouldn't have thought it possible if I told you the name of the institution. Aside from his name, he was also active in shaping their employability while they were still in the program, i.e., by encouraging them to clean up with fellowships and funding, regular conference attendance, helping form an interesting and viable dissertation topic, making sure they do a popular teaching field, etc. If your advisor is a competent historian AND cares about their students, you're in better shape than most. If in doubt, you should talk to your advisor about how their past advisees have fared in the job market, and what they did to prep them.
if you're still worried, think about what you'd be doing with these next few years if you didn't go into graduate school. I'd be either unemployed or working crappy retail/janitorial jobs. I guess I could try to apply to be a store executive (manager) at Target, since all you need is a BA, but I'd probably kill myself six months in. I can't go into professional school for law or teaching since the lawyer market is wretched and my state is constantly laying off school teachers. Since I'm fully funded, going to grad school is a smart idea for me, I'll still be barely making a living but at least I'm doing something I genuinely enjoy. If I don't get hired for a tenure job, those will be at least 5-8 years I where wasn't cleaning up vomit... If you have real career options, you should seriously consider them, but if you're in my boat, you might as well go through with it if it's free.
edit: I'm attending graduate school because I genuinely want to be a historian, not just to escape the shitty job market. I am aware that graduate school is grueling and that the attrition rate is massive.
