The Borough of Princeton was a borough until December 31, 2012, that is now one of the two former municipalities making up Princeton, New Jersey. It was located in Mercer County, New Jersey, and was completely surrounded by the former Princeton Township, from which it was formed in 1894. As of the 2010 United States Census, the borough had a population of 12,307, reflecting a decline of 1,896 (-13.3%) from the 14,203 counted in the 2000 Census, which had in turn increased by 2,187 (+18.2%) from the 12,016 counted in the 1990 Census.