Franklin Park is an unincorporated community and census-designated place (CDP) located within Franklin Township, in Somerset County, New Jersey, United States. As of the 2010 United States Census, the CDP's population was 13,295. Route 27 (historically known as Old Road/King's Highway and once part of the Lincoln Highway system) bisects the village and serves as the dividing line between the two counties. The adjacent sections of South Brunswick and North Brunswick, Middlesex County on the east side of Route 27 are also known as Franklin Park, but are not included within the CDP's boundaries.
The area is served as United States Postal Service ZIP code 08823. Most of the 2001 anthrax attacks letters had the address of Franklin Park.
The original name for Franklin Park was "Six Mile Run", which was named for the tributary of the Millstone River that flows through the area and first came to importance about 1710.
In that year a congregation of the Six Mile Run Reformed Church was formed making it the oldest congregation in Franklin Township and remains an important part of the community. The first building was replaced by a new building in 1766 and was later replaced in 1817 by a third structure on the same site. The current building replaced the 1817 church that was destroyed by fire in 1879. The Frelinghuysen Memorial Chapel was added in 1907 and the Fellowship Hall was dedicated in 1958.
Franklin Park, then Six Mile Run, served as the first site of the Somerset County Courthouse and jail from 1714 until 1737 when a fire destroyed the building and the county seat was moved to Millstone, New Jersey. Occasionally Franklin Park was referred to as Somerset Courthouse during the time the courthouse was located here. A commemorative marker is located on Route 27 between Clover Place and Bennington Parkway near the original courthouse site.
Several early taverns were established here and welcomed travelers using King's Highway while headed towards New Brunswick and New York City going north and Princeton, Trenton and Philadelphia going south.