Lyndhurst is a township in Bergen County, New Jersey, United States. As of the United States 2000 Census, the township population was 19,383. 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.