I know Montgomery County has well defined ordinances. A quick google search turns up little for Fairfax.
http://www6.montgomerycountymd.gov/dectmpl.asp?url=/Content/dep/community/generator.asp
Most people think a generator is a generator. They are not. Some are actually quite noisy. All my neighbors have el cheapo ones and they are probably twice as loud as mine. When I goto racetracks, it's common courtesy to shut them off at night so people can sleep, but obviously it's a different situation we are in. But because of that courtesy, I ended up buying a fairly quiet inverter generator. Rated at 58dB @ 7 meters away. Most cheap generators are 75-85dB, so quite a big difference.