What is now Green Brook was originally created as North Plainfield Township on April 2, 1872, from portions of Warren Township. Portions of the township were taken to form North Plainfield borough (June 9, 1885) and Watchung (March 23, 1926). Green Brook was incorporated as a township by an Act of the New Jersey Legislature on November 8, 1931, replacing North Plainfield Township, based on the results of a referendum held that same day.
Green Brook shares ZIP code 08812 with Dunellen.
The township's unofficial motto is "Small Enough to Know You, Large Enough to Get Things Done".
There were 1,893 households out of which 37.0% had children under the age of 18 living with them, 69.0% were married couples living together, 7.9% had a female householder with no husband present, and 20.3% were non-families. 15.9% of all households were made up of individuals and 6.2% had someone living alone who was 65 years of age or older. The average household size was 2.84 and the average family size was 3.20.
In the township the population was spread out with 24.3% under the age of 18, 4.8% from 18 to 24, 30.5% from 25 to 44, 24.8% from 45 to 64, and 15.6% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 91.7 males. For every 100 females age 18 and over, there were 89.0 males.
The median income for a household in the township was $80,644, and the median income for a family was $87,744. Males had a median income of $52,147 versus $46,434 for females. The per capita income for the township was $37,290. About 1.7% of families and 2.4% of the population were below the poverty line, including 0.9% of those under age 18 and 5.5% of those age 65 or over.
Current members of the Green Brook Township Committee are Mayor Kenneth Herrmann, Deputy Mayor Jerry Searfoss, Melonie K. Marano, Frank Mercuri and John Richards.
Green Brook Township took its name from the powerful stream called the Green Brook that rises in the Watchung Mountains several miles away, feeding from many smaller brooks and ponds along the way, in a southwesterly direction for a distance of fifteen miles, into the Bound Brook then into the Raritan River.
Also contained within the boundaries of this community is Washington Rock State Park, which commemorates the spot where George Washington and Marquis de Lafayette watched the movement of the British soldiers during the American Revolutionary War, mainly the months of May and June 1777. Washington Rock State Park was commissioned on March 17, 1913 and is about 34 acres in size.
For the 1998-99 school year, Irene E. Feldkirchner Elementary School was recognized with the Blue Ribbon Award from the United States Department of Education, the highest honor that an American school can achieve.
Green Brook's public school students in grades 9-12 attend public school at Watchung Hills Regional High School in Warren Township. Students from Green Brook and from the neighboring communities of Watchung and Warren Township (in Somerset County) and Long Hill Township (in Morris County) attend the school.. As of the 2005-2006 school year, there were over 1,900 students attending. Watchung Hills underwent some recent remodeling and now has a new gym, auditorium, and classrooms.