Jamesburg was formed as a borough by an Act of the New Jersey Legislature on March 19, 1887, when it was created from portions of Monroe Township, based on the results of a referendum held on March 15, 1887. Jamesburg's incorporation was confirmed April 15, 1915.
As of the census of 2000, there were 6,025 people, 2,176 households, and 1,551 families residing in the borough. The population density was 7,148.2 people per square mile (2,769.4/km²). There were 2,240 housing units at an average density of 2,657.6/sq mi (1,029.6/km²). The racial makeup of the borough was 82.82% White, 8.83% African American, 0.20% Native American, 2.22% Asian, 3.80% from other races, and 2.12% from two or more races. Hispanic or Latino of any race were 10.06% of the population.
There were 2,176 households out of which 35.4% had children under the age of 18 living with them, 54.7% were married couples living together, 12.1% had a female householder with no husband present, and 28.7% were non-families. 22.4% of all households were made up of individuals and 6.9% had someone living alone who was 65 years of age or older. The average household size was 2.70 and the average family size was 3.18.
In the borough the population was spread out with 24.6% under the age of 18, 7.5% from 18 to 24, 35.6% from 25 to 44, 21.5% from 45 to 64, and 10.7% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 95.0 males. For every 100 females age 18 and over, there were 92.7 males.
The median income for a household in the borough was $59,461, and the median income for a family was $67,887. Males had a median income of $45,019 versus $33,333 for females. The per capita income for the borough was $23,325. About 3.0% of families and 3.5% of the population were below the poverty line, including 5.1% of those under age 18 and 3.9% of those age 65 or over.
Jamesburg hosts CR 522, which then passes through Monroe at both ends. Jamesburg's busiest roads are Pergola Avenue (County Route 612), Buckelew Avenue (CR 522), Perrineville Road (County Route 625), Half Acre Road (County Route 615), and Forsgate Drive (County Route 612). Motorists can use 612 as a route to connect to Route 32 or the New Jersey Turnpike to CR 520.
Jamesburg is accessible from Turnpike Exit 8A via Forsgate Drive (County Route 612).