Jamesburg is a borough in Middlesex County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 5,915, reflecting a decline of 110 (-1.8%) from the 6,025 counted in the 2000 Census, which had in turn increased by 731 (+13.8%) from the 5,294 counted in the 1990 Census.
Jamesburg was formed as a borough by an Act of the New Jersey Legislature on March 19, 1887, when it was created from portions of Monroe Township, based on the results of a referendum held on March 15, 1887. Jamesburg's incorporation was confirmed on April 15, 1915. It was named for James Buckelew, a local business leader.