Hackettstown, NJ has a population of 9,585 and is the 4,063rd largest city in the United States. The population density is 2,654 per sq mi which is 265277% higher than the New Jersey average and 2829% higher than the national average. The median age in Hackettstown is 36 which is approximately 9% lower than the New Jersey average of 40. In Hackettstown, 53% of the population over 15 years of age are married, 73% speak English and 16% speak Spanish. 58% of Hackettstown residents were born in New Jersey, 19% were born out of state, 1% were born outside of the United States and 21% were foreign born.