What is now Mount Holly was originally formed as Northampton on November 6, 1688. Northampton was incorporated as one of New Jersey's initial 104 townships by an Act of the New Jersey Legislature on February 21, 1798. Portions of the township were taken to form Little Egg Harbor Township , Pemberton borough , Coaxen Township , Westampton Township and Lumberton Township . The township was renamed Mount Holly as of November 6, 1931, based on the results of a referendum held three days earlier.
As of the census of 2000, there were 10,728 people, 3,903 households, and 2,583 families residing in the township. The population density was 3,750.8 people per square mile (1,448.3/km²). There were 4,248 housing units at an average density of 1,485.2/sq mi (573.5/km²). The racial makeup of the township was 68.68% White, 21.57% African American, 0.42% Native American, 1.37% Asian, 0.07% Pacific Islander, 4.77% from other races, and 3.12% from two or more races. Hispanic or Latino of any race were 8.78% of the population.
There were 3,903 households out of which 32.0% had children under the age of 18 living with them, 44.0% were married couples living together, 17.3% had a female householder with no husband present, and 33.8% were non-families. 27.2% of all households were made up of individuals and 10.0% had someone living alone who was 65 years of age or older. The average household size was 2.64 and the average family size was 3.20.
In the township the population was spread out with 26.3% under the age of 18, 9.4% from 18 to 24, 32.2% from 25 to 44, 19.6% from 45 to 64, and 12.4% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 99.7 males. For every 100 females age 18 and over, there were 96.6 males.
The median income for a household in the township was $43,284, and the median income for a family was $52,000. Males had a median income of $38,186 versus $27,425 for females. The per capita income for the township was $19,672. About 6.8% of families and 9.9% of the population were below the poverty line, including 11.4% of those under age 18 and 10.4% of those age 65 or over.
Mount Holly is accessible at exit 5 of the New Jersey Turnpike via County Route 541.
New Jersey Transit provides bus service to Philadelphia on the 317, 409 and 413 bus routes.