Regarding the location, it could be somewhere up in the Mid-West Region of the U.S.
(Indiana, Ohio, Kentucky, Pennsylvania, and the surrounding states would really all work) There are hills and plains alike in these areas, as well as tornadoes and floods. The weather ranges from really hot to really cold so that allows for a lot of weather freedom. It's often cloudy, but the constant clouds could just be that it's Spring or Summer... We (or at least I) haven't really experienced Winter yet so I'm guessing it hasn't been over a year in the RP, so seasons could be adjusted...
Also for the military thing to work, it should probably be in the U.S... Considering they have the most hands-on/powerful military... No dinky Peruvian military would give a crap about petty infected towns, or at least wouldn't have countless Apaches and jets flying over unmarked areas.
Plus if we add a farm this would really support these locations, as they're goddamn full of farms.