The territory that would become Clark was originally a part of several of the early villages of the State and of Union County, but it was in 1858 after the village of Rahway incorporated itself into a city, that the land of present-day Clark, officially became a community. The City of Rahway designated this land as the 5th Ward of Rahway. Clark was incorporated as a township by an Act of the New Jersey Legislature on March 23, 1864, from portions of Rahway. The Township was named for Abraham Clark, a signer of the Declaration of Independence. Portions of the township were taken to form Cranford Township and Winfield Township .
New Jersey Monthly magazine ranked Clark as its 33rd best place to live in its 2008 rankings of the "Best Places To Live" in New Jersey.
As of the census of 2000, there were 14,597 people, 5,637 households, and 4,126 families residing in the township . The population density was 3,359.6 people per square mile (1,298.6/km²). There were 5,709 housing units at an average density of 1,314.0/sq mi (507.9/km²). The racial makeup of the township was 95.61% White, 0.30% African American, 0.01% Native American, 2.75% Asian, 0.63% from other races, and 0.69% from two or more races. Also Hispanic or Latino of any race were 3.67% of the population.
There were 5,637 households out of which 28.1% had children under the age of 18 living with them, 61.4% were married couples living together, 9.0% had a female householder with no husband present, and 26.8% were non-families. 24.1% of all households were made up of individuals and 12.9% had someone living alone who was 65 years of age or older. The average household size was 2.56 and the average family size was 3.07.
In the township the population was spread out with 20.8% under the age of 18, 5.4% from 18 to 24, 27.6% from 25 to 44, 24.5% from 45 to 64, and 21.7% who were 65 years of age or older. The median age was 43 years. For every 100 females there were 90.5 males. For every 100 females age 18 and over, there were 86.4 males.
The median income for a household in the CDP was $65,019, and the median income for a family was $77,291. Males had a median income of $54,543 versus $36,361 for females. The per capita income for the township was $29,883. About 1.0% of families and 1.7% of the population were below the poverty line, including 2.0% of those under age 18 and 2.7% of those age 65 or over.
The Clark Circle currently connects Central Avenue, Brant Avenue, Valley Road, and the Garden State Parkway via Exit 135.
The Lehigh Valley Railroad served the town with a passenger station in the Picton section. The rail line remains active under Conrail's auspices. A spur line, the Bloodgood Branch, still serves one customer.
New Jersey Transit provides bus service to New York City and points in-between. The 112 route provides service to the Port Authority Bus Terminal in Midtown Manhattan.
Newark Liberty International Airport is approximately 11 miles from Clark.