Lyndhurst was originally formed as Union Township on February 19, 1852 from portions of Harrison Township. On May 15, 1917, the area was incorporated by an Act of the New Jersey Legislature as the Township of Lyndhurst, based on the results of a referendum held one week earlier.
As of the census of 2000, there were 19,383 people, 7,877 households, and 5,206 families residing in the township. The population density was 4,169.7 people per square mile (1,609.4/km). There were 8,103 housing units at an average density of 1,743.1/sq mi (672.8/km). The racial makeup of the township was 89.94% White, 9.0% Hispanic or Latino, 5.40% Asian, 0.61% African American, 0.05% Native American, 0.01% Pacific Islander, 1.95% from two or more races, and 2.05% from other races.
As of the 2000 census, 33.8% of township residents were of Italian ancestry, the 19th-highest percentage of any municipality in the United States, and eighth-highest in New Jersey, among all places with more than 1,000 residents identifying their ancestry.
There were 7,877 households out of which 25.8% had children under the age of 18 living with them, 51.1% were married couples living together, 11.2% had a female householder with no husband present, and 33.9% were non-families. 28.8% of all households were made up of individuals and 12.6% had someone living alone who was 65 years of age or older. The average household size was 2.46 and the average family size was 3.06.
In the township the population was spread out with 19.1% under the age of 18, 7.6% from 18 to 24, 32.4% from 25 to 44, 23.1% from 45 to 64, and 17.7% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 91.1 males. For every 100 females age 18 and over, there were 88.2 males. Lyndhurst has the highest proportion of single females ages 18–25.
The median income for a household in the township was $53,375, and the median income for a family was $63,758. Males had a median income of $42,359 versus $35,429 for females. The per capita income for the township was $25,940. About 2.8% of families and 4.6% of the population were below the poverty line, including 4.2% of those under age 18 and 7.6% of those age 65 or over.
There are two train stations in Lyndhurst. Lyndhurst Station and Kingsland Station are both served by New Jersey Transit's Main Line, with service to Hoboken Terminal, New York Penn Station via the connecting service at Secaucus Junction, and Midtown Manhattan and the World Trade Center Station via PATH.
New Jersey Transit bus routes 76, 191, 192, 193, and 195 and Decamp Bus Lines routes 32, 44 and 99 serve Lyndhurst.
Route 17, County Route 507, and the western spur of the New Jersey Turnpike pass through Lyndhurst. Route 3 is at the northern border of Lyndhurst. Also Route 21 on the other side.