Helmetta is a borough in Middlesex County, in the U.S. state of New Jersey. The borough is located in the heart of the Raritan Valley region, with Manalapan Brook flowing through the center of the community. As of the 2020 United States census, the borough's population was 2,455, its highest decennial count ever and an increase of 277 (+12.7%) from the 2010 census count of 2,178, which in turn reflected an increase of 353 (+19.3%) from the 1,825 counted in the 2000 census. The community was established around a snuff mill opened in the 1820s that was acquired by George Washington Helme in the 1880s.

Manalapan Brook is a tributary of the South River in Monmouth and Middlesex counties, New Jersey in the United States.