Roselle Park is a borough in Union County, in the U.S. state of New Jersey. As of the 2020 United States census, the borough's population was 13,967, an increase of 670 from the 2010 census count of 13,297, which in turn reflected an increase of 16 from the 13,281 counted in the 2000 census. Roselle Park was incorporated as a borough by an act of the New Jersey Legislature on March 22, 1901, from portions of Union Township.