Listen to it or record it, then listen for street names, call signs, names of towns, cities, counties. If you can get a city or a county, Google the name with the frequency. Example- 39.980 Custer County. This is the only way. You can get a general idea of where it is coming from if they give a time (time zone) or if they have an accent (NY/NJ). So get a pen and paper and get ready to start writing what you hear then Google it!
If you can pick up a Call Sign, then go to this web-site http://fjallfoss.fcc.gov/General_Menu_Reports/engineering_search.cfm?accessible=NO ,and put the frequency in and see if you can locate what you are listening to that way. Just looking thru the list of users for that frequency, there are a bunch of Fire Companies listed in PA, IL, OH, NY, SC, WV, VA and other locals way west of you. Good luck... I know how cool that is to hear something like that and want to know where it is coming from. Had something like that happen to me years ago when I was a volunteer firefighter. We had Minitor voice pagers and I had mine in "Open" mode one night and heard a fire dispatch acknowledging a truck back in quarters. Unfortunately, I didn't get enough of the call sign to make a definite ID on where it was coming from. And this was in VHF Hi band! Extrordinary conditions at the time!