Summit is the northernmost city of Union County, in the U.S. state of New Jersey, located within the New York metropolitan area. Situated on a ridge in northern-central New Jersey, the city is located within the Raritan Valley and Rahway Valley regions, and also borders both Essex and Morris counties in the Passaic Valley region. Summit is a commercial hub and commuter town for New York City. As of the 2020 United States census, the city's population was 22,719, an increase of 1,262 (+5.9%) from the 2010 census count of 21,457, which in turn reflected an increase of 326 (+1.5%) from the 21,131 counted in the 2000 census.

Union County is a county in the northern part of the U.S. state of New Jersey. As of the 2020 United States census, the county was the state's seventh-most-populous county with a population of 575,345, its highest decennial count ever and an increase of 38,846 (+7.2%) from the 2010 census count of 536,499. Its county seat is Elizabeth, which is also the most populous municipality in the county, with a 2020 census population of 137,298, and the largest by area, covering 13.46 square miles (34.9 km2). The county serves as a transition point between the Central Jersey and North Jersey regions of the state.