Do you mean a house/neighborhood within the Town of Herndon, or just with a Herndon zip code?
Once they opened up the Oak Hill post office, a whole bunch of places that formerly used Herndon mailing addresses switched to using Oak Hill instead, because having a Herndon address was harmful to their real estate values.
Stepping back a few decades, the Town of Herndon and Fairfax County did a land swap back in the mid-80s that put Worldgate within the town's borders. See
https://www.washingtonpost.com/archive/local/1986/05/29/fairfax-board-and-herndon-officials-agree-unofficially-on-land-exchange/a39b3a0d-fece-4b4b-b8f7-785cf5064d0f/