Kenilworth was incorporated as a borough by an Act of the New Jersey Legislature on May 13, 1907, from portions of Cranford and Union Township, based on the results of a referendum held on June 18, 1907.
As of the census of 2000, there were 7,675 people, 2,854 households, and 2,117 families residing in the borough. The population density was 3,584.9 people per square mile (1,384.7/km²). There were 2,926 housing units at an average density of 1,366.7/sq mi (527.9/km²). The racial makeup of the borough was 92.30% White, 2.30% African American, 0.25% Native American, 2.88% Asian, 1.80% from other races, and 1.38% from two or more races. Hispanic or Latino of any race were 8.64% of the population.
There were 2,854 households out of which 28.6% had children under the age of 18 living with them, 58.4% were married couples living together, 11.9% had a female householder with no husband present, and 25.8% were non-families. 21.4% of all households were made up of individuals and 11.0% had someone living alone who was 65 years of age or older. The average household size was 2.69 and the average family size was 3.15.
In the borough the population was spread out with 20.8% under the age of 18, 6.9% from 18 to 24, 30.8% from 25 to 44, 23.3% from 45 to 64, and 18.2% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 94.2 males. For every 100 females age 18 and over, there were 90.7 males.
The median income for a household in the borough was $59,929, and the median income for a family was $66,500. Males had a median income of $40,808 versus $34,698 for females. The per capita income for the borough was $24,343. About 1.9% of families and 2.0% of the population were below the poverty line, including 2.2% of those under age 18 and 3.2% of those age 65 or over.
New Jersey Transit provides bus service to the Port Authority Bus Terminal in Midtown Manhattan in New York City and to New Jersey points, including the city of Elizabeth and nearby Union County College in Cranford.
The Rahway Valley Railroad passed through the community but is currently out of service. The headquarters of the railroad were also located in the town.
Newark Liberty International Airport is approximately eight miles from Kenilworth.