While New Jersey was an English colony, Mendham Township was formed as a township on March 29, 1749, from portions of Hanover Township, Morris Township, and Rockaway Township. Sites had been established by settlers from the early 1700s and villages named.
After the American War of Independence, the township was incorporated under the same name by an Act of the New Jersey Legislature on February 21, 1798. Portions of the township were taken to create Randolph Township on January 1, 1806. The village of Mendham, adopted the newly created borough form of government on May 15, 1906 and withdrew from the governance of the township council.
There were 1,788 households out of which 47.0% had children under the age of 18 living with them, 80.2% were married couples living together, 4.0% had a female householder with no husband present, and 13.9% were non-families. 11.1% of all households were made up of individuals and 4.6% had someone living alone who was 65 years of age or older. The average household size was 3.01 and the average family size was 3.27.
In the township the population was spread out with 32.0% under the age of 18, 3.6% from 18 to 24, 23.8% from 25 to 44, 29.9% from 45 to 64, and 10.8% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 96.8 males. For every 100 females age 18 and over, there were 94.1 males.
The median income for a household in the township was $136,174, and the median income for a family was $146,254. Males had a median income of $100,000 versus $57,946 for females. The per capita income for the township was $61,460. About 1.4% of families and 1.8% of the population were below the poverty line, including 2.3% of those under age 18 and 0.9% of those age 65 or over.
Mendham Township is ranked as the 17th wealthiest community in the state of New Jersey. It is located on the southern border of the 10th wealthiest US county, Morris County.
Members of the Mendham Township Committee are Mayor Phyllis Florek (term ends December 31, 2010), Deputy Mayor Brian Phelan (2010), Frank Cioppettini (2009), Richard Krieg (2008), Jack J. Schrier (2009).
Students in grades 9-12 for public school attend West Morris Mendham High School, which is located in Mendham Borough and is part of the West Morris Regional High School District. Students in the district come from the surrounding Morris County school districts of Chester, Chester Township, Mendham , Mendham Township, and from Washington Township.
The all-boys Delbarton School in neighboring Morris Township also draws a number of Mendham boys in grades 7-12.