Princeton is a borough in Mercer County, in the U.S. state of New Jersey. It was established on January 1, 2013, through the consolidation of the Borough of Princeton and Princeton Township, both of which are now defunct. As of the 2020 United States census, the borough's population was 30,681, an increase of 2,109 (+7.4%) from the 2010 census combined count of 28,572. In the 2000 census, the two communities had a total population of 30,230, with 14,203 residents in the borough and 16,027 in the township.