Lake Braddock Secondary School in Burke, Virginia (which is part of the Fairfax County school system) is the largest public high school in the state with 4072± students (bet they have a heck of a good marching band). In fact, the top 10 largest high schools in Virginia are in or around Fairfax.
Here's the list of the top 5 (by student population) High Schools:
Lake Braddock Secondary School - 4072
Robinson Secondary School - 3974
T.C. Williams High School - 3324
Woodbridge High School 2897
Hayfield Secondary School - 2826
There are over 200 small towns and villages in Virginia with fewer than 1000 residents, but of course they have names like Max Meadows, Meadow View and Sugar Grove (and likely only one or two stoplights). So, the fact that the total populations of any 4 of these hamlets could fit in Lake Braddock with a little room to spare gives you some perspective.