Jacksonville is the county seat of and the most populous community in Onslow County, North Carolina, which is coterminous with the Jacksonville, NC Metropolitan Statistical Area. As of the 2020 census, the population was 72,723, which makes Jacksonville the 14th-most populous city in North Carolina. 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 increasing over the past 80 years, from 783 in the 1930 census to 72,723 in the 2020 census.