Flagtown is an unincorporated community and census-designated place[4] located within Hillsborough Township, in Somerset County, in the U.S. state of New Jersey.

[8] At this point only one train station was marked on the map west of South Branch road between the two rail lines.

Some years later, J. Flagg, a descendant and proprietor of a local tavern had it used as headquarters for the Hillsborough Company in the American Revolutionary War.

The first school was built there about 1725 on a knoll near the future site of the railroad station and it is said that William Parrish taught there.

Flagtown has its own post office (ZIP code 08821) but no house-to-house mailbox delivery, therefore residents have no other option than to have a P.O.

Prior to the establishment of the Hillsborough post office, Neshanic had covered partial Flagtown home delivery.

The Flagtown post office is small (despite some expansion work done within the last 10 years), and usually staffed by one or two workers at any given time, who take care of all jobs themselves.

There's very limited parking, as the post office is part of an apartment/storefront, sharing the building with a small local deli and two residential apartments.