Most of this area is Oak Hill, but some parts are Fairfax, Herndon, or Reston. The area where a lot of construction is taking place (from Vail Road to Franklin Farm Road is considered Oak Hill. That is a fairly new Postal Address. The Franklin Farm neighborhood used to be Herndon, is now Oak Hill, but many homes listed in the neighborhood are still listed as Herndon.
In Fairfax County, which this whole area you are talking about is in, different areas are often just postal addresses as opposed to cities or towns. There are no cities or towns along West Ox Road until you get to the town of Herndon. But many areas not in the town of Herndon are still referred to as "Herndon" , but it is only in the sense of the postal address and they are not part of the town. This is obviously pretty confusing.
In terms of schools and taxes the whole area you refer to is Fairfax County. Fairfax County runs the schools and collects the taxes in the area, even if the house is in a town (though the town may collect additional taxes). Towns are part of the county.
Cities are not a part of the county, but separate entities all together. The closest example is Fairfax City. They collect their own (lower) taxes, and residents do not pay county taxes. Fairfax City does, however, contact with Fairfax County to run City schools. So even Fairfax City is part of the Fairfax County School System.
I hope this helps and does not confuse you more. I'd be glad to run a geographical search for you that would find houses in a certain area regardless of how they are listed. Contact me if you would like me to do that.
I drive West Ox very often also. It will be nice when the construction is done.