There are 8 US Post Offices in Northumberland County serving a total of 14,509 residents equating to 1,814 residents per post office. It's estimated that approximately 23,158 packages are handled across the 8 county post offices annually. Northumberland County is a county located in the Commonwealth of Virginia. As of the 2010 census, the population was 12,330. Its county seat is Heathsville. The county is located on the Northern Neck and is part of the Northern Neck George Washington Birthplace AVA winemaking appellation."