WebHackettstown 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. . [19] As of the 2020 United States census , the town's population was 10,248, [9] [10] an increase of 524 (+5.4%) from the 2010 census count of 9,724, [20] [21] which in turn reflected a decline of ...