Belvidere was incorporated as a town by an Act of the New Jersey Legislature on April 7, 1845, from portions of Oxford Township, based on the results of a referendum held that day.
Belvidere is located in the eastern section of the Lehigh Valley.
As of the census of 2000, there were 2,771 people, 1,088 households, and 716 families residing in the town. The population density was 2,091.7 people per square mile (810.5/km²). There were 1,165 housing units at an average density of 879.4/sq mi (340.8/km²). The racial makeup of the town was 98.02% White, 0.51% African American, 0.04% Native American, 0.51% Asian, 0.25% from other races, and 0.69% from two or more races. Hispanic or Latino of any race were 2.31% of the population.
There were 1,088 households out of which 36.4% had children under the age of 18 living with them, 52.0% were married couples living together, 9.7% had a female householder with no husband present, and 34.1% were non-families. 28.5% of all households were made up of individuals and 11.1% had someone living alone who was 65 years of age or older. The average household size was 2.54 and the average family size was 3.17.
In the town the population was spread out with 28.1% under the age of 18, 6.1% from 18 to 24, 32.2% from 25 to 44, 20.7% from 45 to 64, and 12.8% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 92.0 males. For every 100 females age 18 and over, there were 88.5 males.
The median income for a household in the town was $52,792, and the median income for a family was $62,212. Males had a median income of $41,800 versus $31,444 for females. The per capita income for the town was $23,231. About 1.3% of families and 3.4% of the population were below the poverty line, including 0.4% of those under age 18 and 10.4% of those age 65 or over.