Roselle (, row-ZELL) is a borough located in Union County in the state of New Jersey, United States. As of the 2010 United States Census, the borough's population was 21,085, reflecting a decline of 189 (-0.9%) from the 21,274 counted in the 2000 Census, which had in turn increased by 960 (+4.7%) from the 20,314 counted in the 1990 Census.
On January 19, 1883, the world's first electric lighting system employing overhead wires began service in Roselle. It had been built by Thomas Edison to demonstrate that an entire community could be lit by electricity. This success encouraged the installation of electric lighting in numerous other villages and cities. The First Presbyterian Church, located on the corner of West 5th Avenue and Chestnut Street, was the first church in the United States to be lit by electricity, and the second in the world after the City Temple church in London.
Roselle was incorporated on December 20, 1894, at the height of the Boroughitis phenomenon sweeping through New Jersey at the time, based on the results of a referendum held two days earlier, from portions of Linden. Roselle's name is derived from the Roselle Land Improvement Company, which was created in 1866 to lay out a community around the Mulford Station on the Central Railroad of New Jersey. The name "Roselle" is said to have been based on the company's founder, John Conklin Rose or from John Pierre Roselle, a friend of the railroad's president.
According to the United States Census Bureau, the borough had a total area of 2.664 square miles (6.899 km2), including 2.651 square miles (6.866 km2) of land and 0.013 square miles (0.033 km2) of water (0.47%),
Unincorporated communities, localities and place names located partially or completely within the borough include Aldene.
The borough is bordered by the Union County municipalities of Roselle Park to the north, Linden to the south and Cranford to the west and Elizabeth, along the edges of Warinanco Park, to the east. Morses Creek runs through the borough.
The 2010 United States Census counted 21,085 people, 7,407 households, and 5,096.016 families in the borough. The population density was 7,953.5 per square mile (3,070.9/km2).