Hackettstown is a town in Warren County, in the U.S. state of New Jersey. It is perhaps best known as the home to the US headquarters of Mars, Inc.. As of the 2020 United States census, the town's population was 10,248, an increase of 524 (+5.4%) from the 2010 census count of 9,724, which in turn reflected a decline of 679 (−6.5%) from the 10,403 counted in the 2000 census.

Warren County is a county located in the U.S. state of New Jersey. According to the 2020 census, the county was the state's 19th-most populous county, with a population of 109,632, its highest decennial count ever and an increase of 940 (+0.9%) from the 2010 census count of 108,692, which in turn reflected an increase of 6,255 (+6.1%) from 102,437 counted at the 2000 census. The county is part of the North Jersey region of the state.