Glen Gardner is a borough in Hunterdon County, in the U.S. state of New Jersey. As of the 2020 United States census, the borough's population was 1,682, a decrease of 22 (−1.3%) from the 2010 census count of 1,704, which in turn reflected a decline of 198 (−10.4%) from the 1,902 counted in the 2000 census.

Route 31 is a state highway in New Jersey, United States. It runs 48.93 mi (78.75 km) from U.S. Route 1 Business /US 206 in Trenton, Mercer County, north to an intersection with US 46 in Buttzville in White Township, Warren County. Along the way, Route 31 heads through the communities of Flemington, Clinton, and Washington. Most of the highway is state-maintained; however, the section within the city limits of Trenton is maintained by the city. Much of Route 31 is a two-lane highway that passes through farmland, woodland, and mountainous areas. Two portions of the route—from Trenton to Pennington and from Ringoes to Clinton—consist of more development.