Middlesex is a borough in Middlesex County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 13,635 reflecting a decline of 82 (-0.6%) from the 13,717 counted in the 2000 Census, which had in turn increased by 662 (+5.1%) from the 13,055 counted in the 1990 Census.
Middlesex was incorporated as a borough by an act of the New Jersey Legislature on April 9, 1913, from portions of Piscataway, based on the results of a referendum held on May 6, 1913. The borough's name derives from Middlesex, England.
The Harris Lane School was a one-room schoolhouse that was the oldest school in Middlesex County, dating back to its construction in the 1790s. The original Pierce School was known as the East Bound Brook School House and The Parker House was also used for education until it was converted into a two-family house. As the Borough grew new schools were constructed to accommodate many more students. Our Lady of Mt. Virgin School was the first parochial school built in 1954.
In 1905, the Lincoln section of Middlesex organized a volunteer fire company and that set the organization of four other fire companies in the Borough.
Middlesex was a portion of Piscataway Township, until May 6, 1913 when it was incorporated as a separate entity through the action of the state legislature and local referendum. George Harris was elected as the first mayor and the first borough council was elected at the same time.