Milltown was incorporated as a borough by an Act of the New Jersey Legislature on January 29, 1889, from portions of North Brunswick Township, based on the results of a referendum held three day earlier. The borough was incorporated by resolution of the borough council on May 2, 1896. A portion of East Brunswick Township was annexed in 1902.
As of the 2000 Census, the center of population for New Jersey was located in Milltown, at Milltown Road, just east of the New Jersey Turnpike (see map of location).
Miltown (meprobamate), the groundbreaking anxiolytic and sedative drug that first came to market in the mid-1950s, was named after the town of Milltown.
As of the census of 2000, there were 7,000 people, 2,627 households, and 1,943 families residing in the borough. The population density was 4,452.0 people per square mile (1,721.5/km²). There were 2,670 housing units at an average density of 1,698.1/sq mi (656.6/km²). The racial makeup of the borough was 93.86% White, 0.76% African American, 0.16% Native American, 3.07% Asian, 1.16% from other races, and 1.00% from two or more races. Hispanic or Latino of any race were 3.73% of the population.
There were 2,627 households out of which 31.7% had children under the age of 18 living with them, 60.9% were married couples living together, 9.9% had a female householder with no husband present, and 26.0% were non-families. 21.4% of all households were made up of individuals and 9.7% had someone living alone who was 65 years of age or older. The average household size was 2.66 and the average family size was 3.12.
In the borough the population was spread out with 22.9% under the age of 18, 6.8% from 18 to 24, 29.5% from 25 to 44, 25.1% from 45 to 64, and 15.7% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 93.2 males. For every 100 females age 18 and over, there were 90.2 males.
The median income for a household in the borough was $68,429, and the median income for a family was $77,869. Males had a median income of $50,338 versus $38,220 for females. The per capita income for the borough was $29,996. About 1.3% of families and 2.3% of the population were below the poverty line, including 3.3% of those under age 18 and 1.3% of those age 65 or over.