Kearny was originally formed as a township by an Act of the New Jersey Legislature on April 8, 1867, from portions of Harrison Township. Portions of the township were taken on July 3, 1895, to form East Newark. Kearny was incorporated as a town on January 19, 1899, based on the results of a referendum held two days earlier.
As of the census of 2000, there were 40,513 people, 13,539 households, and 9,802 families residing in the town. The population density was 4,433.2 people per square mile (1,711.4/km²). There were 13,872 housing units at an average density of 1,518.0/sq mi (586.0/km²). The racial makeup of the town was 75.75% White, 3.97% African American, 0.37% Native American, 5.50% Asian, 0.07% Pacific Islander, 10.04% from other races, and 4.31% from two or more races. Hispanic or Latino of any race were 27.34% of the population.
There were 13,539 households out of which 34.6% had children under the age of 18 living with them, 53.8% were married couples living together, 13.2% had a female householder with no husband present, and 27.6% were non-families. 21.8% of all households were made up of individuals and 8.8% had someone living alone who was 65 years of age or older. The average household size was 2.81 and the average family size was 3.28.
In the town the population was spread out with 21.5% under the age of 18, 10.7% from 18 to 24, 35.7% from 25 to 44, 21.3% from 45 to 64, and 10.9% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 106.6 males. For every 100 females age 18 and over, there were 107.0 males.
The median income for a household in the town was $47,757, and the median income for a family was $54,596. Males had a median income of $38,672 versus $30,620 for females. The per capita income for the town was $20,886. About 6.1% of families and 8.6% of the population were below the poverty line, including 9.1% of those under age 18 and 10.0% of those age 65 or over.
New Jersey Transit offers bus service to the Port Authority Bus Terminal in Midtown Manhattan and to other New Jersey communities. Bus service to Newark is available on the 1, 39, 40, 43, 76 and 80 routes.
The Belleville Turnpike (Route 7) forms the northern border of the town with North Arlington. Kearny Avenue passes through the town and continues north as Route 17. The Essex Freeway (I-280) passes through the boro and ends at Interstate 95(W)/New Jersey Turnpike at Exit 15W. A toll gate (the 15W toll gate) is located in Kearny, with a total of 14 lanes at the gate.
The closest airport with scheduled passenger service is Newark Liberty International Airport, located 6.5 miles away in Newark / Elizabeth.
Kearny was formerly served by rail service at Arlington Station, along the former Boonton Line stretching from Montclair to Hoboken. When the Midtown Direct service and Secaucus Junction were opened, the line was abandoned and service was ended. There is a movement to use the rails of the former Boonton Line, as well as the connecting rails which swing through Harrison and East Newark to the south, to expand the Newark Light Rail service. Phase 1 of the project involves reactivating Arlington Station as the endpoint station for the initial run, which is connected to the Newark Light Rail tracks already through a small spur line that the NLR is using to reach Grove Street Station in Bloomfield. Eventually, the project aims to expand light rail service over these rails to the towns of Bloomfield, Belleville, Glen Ridge, Montclair, Nutley, Clifton, Paterson, East Newark, Harrison and finally to Hoboken, where it will meet up with the Hudson-Bergen Light Rail and establish one light rail system that crawls across Essex County, Passaic County, Hudson County and Bergen County, and allow relatively inexpensive and truly viable alternative to automotive transit in the northern portion of the state.