Hardwick Township was created by Royal Charter on January 22, 1750, from Greenwich Township, while the area was part of Morris County. It became part of the newly-created Sussex County on June 8, 1753. Parts of Hardwick Township were taken on November 11, 1782, to form Independence Township. Hardwick Township was incorporated as a township by an Act of the New Jersey Legislature on February 21, 1798. On November 20, 1824, most of Hardwick Township was transferred to form part of Warren County, with the remainder staying in Sussex County as parts of Green Township and Stillwater Township, which were both created as of December 27, 1824. Frelinghuysen Township was created March 7, 1848, from portions of the township.
The now-defunct Pahaquarry Township was absorbed by Hardwick Township on July 2, 1997. Pahaquarry Township had been created on March 14, 1825, and got its name from the word Pahaquarra, which was a derivation of the Indian word Pahaqualong, which meant "termination of two mountains" and described the mountain or mountainous area that was the area's southern border.
There were 502 households out of which 38.6% had children under the age of 18 living with them, 74.3% were married couples living together, 5.6% had a female householder with no husband present, and 18.3% were non-families. 13.9% of all households were made up of individuals and 5.2% had someone living alone who was 65 years of age or older. The average household size was 2.85 and the average family size was 3.15.
In the township the population was spread out with 26.6% under the age of 18, 5.2% from 18 to 24, 29.1% from 25 to 44, 29.5% from 45 to 64, and 9.6% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 99.7 males. For every 100 females age 18 and over, there were 95.1 males.
The median income for a household in the township was $72,167, and the median income for a family was $76,111. Males had a median income of $56,000 versus $31,875 for females. The per capita income for the township was $30,038. About 0.5% of families and 2.6% of the population were below the poverty line, including 0.5% of those under age 18 and 2.2% of those age 65 or over.
The Hardwick Township Committee consists of Mayor Kevin Duffy (R, term ends December 31, 2009, Deputy Mayor James Perry (R, 2010) and J. Alfred Carrazzone (R, 2008).
Public school students in grades 7 through 12 attend the North Warren Regional High School (1,044 students) in Blairstown, a public secondary high school, serving students from the townships of Blairstown, Frelinghuysen, Hardwick, and Knowlton.