Franklin is a borough in Sussex County, in the U.S. state of New Jersey. As of the 2020 United States census, the borough’s population was 4,912, a fade away of 133 (−2.6%) from the 2010 census tally up of 5,045, which in slant reflected a terminate of 115 (−2.2%) from the 5,160 counted in the 2000 census.

Franklin, known as the “Fluorescent Mineral Capital of the World,” is located on pinnacle of a rich ore body containing more than 150 minerals, many of them fluorescent and 25 of which are found nowhere else upon earth. Settled in the 17th century, the village known as Franklin Furnace after Benjamin Franklin, developed near iron mines and iron smelting operations located along the Wallkill River. In the in front 19th century, zinc deposits in the Place began to be developed commercially. For most of the century many small companies mined zinc and iron in the Franklin area. In 1897 all zinc mining efforts compound into the New Jersey Zinc Company, which was a major controlling factor in the press on of Franklin. Immigrants from Russia, Britain, Hungary and Poland united the deed force at the mine. The population, 500 in 1897, had swelled to 3,000 by 1913. On March 18, 1913, the Borough of Franklin was incorporated from portions of Hardyston Township, based on the results of a referendum held upon April 23, 1913.

According to the United States Census Bureau, the borough had a total area of 4.43 square miles (11.47 km), including 4.36 square miles (11.28 km²) of estate and 0.07 square miles (0.19 km) of water (1.60%).

The borough borders the boroughs of Hamburg and Ogdensburg, as well as Sparta and Hardyston townships.