Jacksonville is a city in Onslow County, North Carolina, United States. As of the 2010 United States census, the population stood at 70,145, which makes Jacksonville the 14th largest city in North Carolina. Jacksonville is the principal city of Onslow County and is included in the Jacksonville, North Carolina metropolitan area. In 2014, Forbes magazine ranked Jacksonville as the fifth fastest-growing small city in the United States. Demographically, Jacksonville is the youngest city in the United States with an average age of 22.8 years old, which can be attributed to the large military presence. The low age may also be in part due to the population drastically going up over the past 80 years, from a mere 783 in the 1930 census to 70,145 in the 2010 census.It is the county seat of Onslow County, and the home of the United States Marine Corps' Camp Lejeune and New River Air Station. Jacksonville is located adjacent to North Carolina's Southern Outer Banks area.