Pennington is a borough in Mercer County, in the U.S. state of New Jersey. The borough is located at the cross-roads between the Delaware Valley region to the southwest and the Raritan Valley region to the northeast. As of the 2020 United States census, the borough's population was 2,802, its highest decennial count ever and an increase of 217 from the 2010 census count of 2,585, which in turn had reflected a decline of 111 from the 2,696 counted in the 2000 census.