Summit is a city in Union County, New Jersey, United States.At the 2010 United States Census, the city’s population was 21,457, reflecting an increase of 326 (+1.5%) from the 21,131 counted in the 2000 Census, which had in turn increased by 1,374 (+7.0%) from the 19,757 counted in the 1990 Census. Summit had the 16th-highest per capita income in the state as of the 2000 Census According to. Since 2008…