Jacksonville, North Carolina, is a city in Onslow County, North Carolina, United States. As of 2009, the population stood at 80,542. Jacksonville is the principal city of and is included in the Jacksonville, North Carolina metropolitan area. Jacksonville is the youngest city in the United States with an average age of 22.8 years old. The low age can be attributed to the large military presence.It is the county seat of Onslow County, and the home of the United States Marine Corps' Marine Corps Base Camp Lejeune and Marine Corps Air Station New River. Jacksonville is located in North Carolina's Inner Banks region. The City is about 1 hour away from the Port City Wilmington.