South Amboy, and Perth Amboy across the Raritan River, are collectively referred to as The Amboys. Signage for Exit 11 on the New Jersey Turnpike refers to "The Amboys" as a destination.
South Amboy has passed through three of the five types of New Jersey municipalities. It was first mentioned on 28 May 1782 in Freeholder minutes as being formed from Perth Amboy Township, and then formally incorporated as a Township on 21 February 1798. Over the next 90 years, portions broke away to form Monroe Township (9 April 1838), Madison Township (2 March 1869; later Old Bridge Township) and Sayreville Township (6 April 1876; later Borough of Sayreville). As of 25 February 1888, South Amboy borough was formed, replacing South Amboy Township. On 11 April 1908, South Amboy was incorporated as a city, replacing South Amboy borough, with a referendum held on 21 July 1908.
As of the census of 2000, there were 7,913 people, 2,967 households, and 2,041 families residing in the city. The population density was 5,102.1 people per square mile (1,971.1/km²). There were 3,110 housing units at an average density of 2,005.3/sq mi (774.7/km²). The racial makeup of the city was 94.22% White, 0.86% African American, 0.19% Native American, 1.38% Asian, 0.03% Pacific Islander, 1.71% from other races, and 1.62% from two or more races. Hispanic or Latino of any race were 6.75% of the population.
There were 2,967 households out of which 32.2% had children under the age of 18 living with them, 48.8% were married couples living together, 14.5% had a female householder with no husband present, and 31.2% were non-families. 25.9% of all households were made up of individuals and 12.3% had someone living alone who was 65 years of age or older. The average household size was 2.65 and the average family size was 3.22.
In the city the population was spread out with 24.3% under the age of 18, 7.7% from 18 to 24, 32.9% from 25 to 44, 21.5% from 45 to 64, and 13.6% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 95.5 males. For every 100 females age 18 and over, there were 92.0 males.
The median income for a household in the city was $50,529, and the median income for a family was $62,029. Males had a median income of $42,365 versus $29,737 for females. The per capita income for the city was $23,598. About 6.7% of families and 7.4% of the population were below the poverty line, including 10.6% of those under age 18 and 6.0% of those age 65 or over.
The South Amboy station provides service on the New Jersey Transit North Jersey Coast Line, with most trains heading to Penn Station in Midtown Manhattan and some heading to Hoboken Terminal. NJ Transit bus service is available on the 815 and 817 routes.