U.S. Route 1 (US 1) is a U.S. Route which parallels the East Coast of the United States, running from Key West, Florida, in the south to Fort Kent, Maine, at the Canadian border in the north. Of the entire length of the route, 66.06 miles (106.31 km) of it runs through New Jersey. It enters the state from Pennsylvania on the Trenton–Morrisville Toll Bridge over the Delaware River in the state capital of Trenton, running through the city on the Trenton Freeway. From here, US 1 continues northeast as a surface divided highway through suburban areas, heading into Middlesex County and passing through New Brunswick and Edison. US 1 merges with US 9 in Woodbridge, and the two routes continue through northern New Jersey as US 1/9 to the George Washington Bridge over the Hudson River in Fort Lee. At this point, the road continues into New York City along with I-95.

Trenton is the capital city of the U.S. state of New Jersey and the seat of Mercer County. It was the capital of the United States from November 1 until December 24, 1784. Trenton and Princeton are the two principal cities of the Trenton–Princeton metropolitan statistical area, which encompasses those cities and all of Mercer County for statistical purposes and constitutes part of the New York combined statistical area by the U.S. Census Bureau. However, Trenton directly borders the Philadelphia metropolitan area to its west, and the city was part of the Philadelphia combined statistical area from 1990 until 2000.