Warren was originally inhabited by the Lenape Native Americans and was settled in the 1720s by European farmers. As early as 1980, it became a refuge for wealthy residents looking to escape nearby New York City. Warren was incorporated as a township by an Act of the New Jersey Legislature on March 5, 1806, from portions of Bernards Township and Bridgewater Township. Portions of the township were taken to from North Plainfield Township as of April 2, 1872. Warren is named for American Revolutionary War patriot, General Joseph Warren, who was killed at the Battle of Bunker Hill.
As of the census of 2000, there were 14,259 people, 4,629 households, and 3,939 families residing in the township. The population density was 725.0 people per square mile (279.9/km²). There were 4,718 housing units at an average density of 239.9/sq mi (92.6/km²). The racial makeup of the township was 86.28% White, 1.26% African American, 0.04% Native American, 10.67% Asian, 0.06% Pacific Islander, 0.41% from other races, and 1.28% from two or more races. Hispanic or Latino of any race were 3.19% of the population.
There were 4,629 households out of which 45.3% had children under the age of 18 living with them, 78.3% were married couples living together, 4.8% had a female householder with no husband present, and 14.9% were non-families. 12.2% of all households were made up of individuals and 5.0% had someone living alone who was 65 years of age or older. The average household size was 3.05 and the average family size was 3.33.
In the township the population was spread out with 29.7% under the age of 18, 4.6% from 18 to 24, 27.5% from 25 to 44, 27.0% from 45 to 64, and 11.2% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 99.1 males. For every 100 females age 18 and over, there were 95.6 males.
The median income for a household in the township was $103,677, and the median income for a family was $121,264. Males had a median income of $80,231 versus $46,356 for females. The per capita income for the township was $49,475. About 0.7% of families and 2.1% of the population were below the poverty line, including 1.4% of those under age 18 and 1.5% of those age 65 or over.