Hopewell is a borough in Mercer County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 1,922, reflecting a decline of 113 from the 2,035 counted in the 2000 Census, which had in turn increased by 67 from the 1,968 counted in the 1990 Census.Hopewell was incorporated as a borough by an act of the New Jersey Legislature on April 14, 1891, from portions of Hopewell Township, based on the results of a referendum held on March 21, 1891. Additional portions of Hopewell Township were annexed in 1915, and the borough was reincorporated in 1924.