There are 12 US Post Offices in Onslow County serving a total of 179,001 residents equating to 14,917 residents per post office. It's estimated that approximately 285,706 packages are handled across the 12 county post offices annually. Onslow County is a county located in the U.S. state of North Carolina. As of the 2010 census, the population was 177,772. Its county seat is Jacksonville. The county was created in 1734 as Onslow Precinct and gained county status in 1739. Onslow County comprises the Jacksonville, NC Metropolitan Statistical Area. The southern border is the coast of the Atlantic Ocean."