A Baldfaced Hornet queen starts a new nest by herself in spring, and as the worker population (her daughters) increases over the course of the season, the nest grows larger (in both population and physical size). Any hornet nest observed this time of year, especially if it's large, has been in that location since late spring or so. Autumn is the time of year that social wasp nests are at their largest.

These wasps ignore people as long as the nest isn't under attack or a perceived threat (mowing too close to a nest in a tree or shrub, bumping into the plant the nest may be attached to, etc.), so they often coexist with people without conflict until their large size in autumn makes them more apparent. Because of that behavior, Baldfaced Hornet nests are often not noticed until this time of year, even though they've existed all summer.

Nests are not re-used from year to year, and by late autumn or early winter, the colony will be dead, and the few surviving young queens will disperse and overwinter in a sheltered spot elsewhere. The fragile paper-like material of the nest will disintegrate on its own due to weather and wildlife. If you can avoid getting too close to the nest for a few more weeks, the issue will resolve itself. Otherwise, the colony can be killed with wasp spray (follow product label directions), either applied yourself or via a hired pest control professional who deals with wasps.

Miri

Yes, they may rebuild if a nest is damaged, though it would be very unusual for any wasp queen to begin a new nest this late in the year, as they would not have enough time to build up young to produce the next generation of queens that overwinter. (The original queen that founded the nest will die this winter.) Perhaps a nest had been started in that location, was damaged by a person or a predator (a bird, perhaps), and is now being repaired. Wasps in the colony were born in that nest (there are cells somewhat like honeycomb inside the paper envelope, which is where the young wasps mature), so that means that a new nest would not be created by workers that originated elsewhere; they only help their sisters and queen to enlarge the nest they were born in. Therefore, if, say, 100 wasps were working collectively to build nest material, those individuals are all from the same nest originally, and if the current nest is too small to have housed 100+ wasps, then there must have been a larger nest there at some point that may have been lost to predation or weather damage.

Miri

You're welcome!