Raritan Town was originally established as a subdivision within Bridgewater Township by act of the New Jersey Legislature on April 3, 1868. After a series of bitter lawsuits between Raritan and Bridgewater in the 1930s and 1940s, the Legislature allowed Raritan to become an independent Borough by an Act on May 12, 1948, based on the results of a referendum passed on June 12, 1948. The new borough incorporated the old town and an additional portion of Bridgewater Township.
The Knox-Porter Resolution ending United States involvement in World War I was signed by President Harding at the estate of New Jersey Senator Joseph Sherman Frelinghuysen, Sr. on July 2, 1921.