Mount Arlington is a borough in Morris County, New Jersey, United States. As of the 2000 United States Census, the borough's population was 5,050, reflecting an increase of 387 (+8.3%) from the 4,663 counted in the 2000 Census, which had in turn increased by 1,033 (+28.5%) from the 3,630 counted in the 1990 Census. It is located on the southeast shore of Lake Hopatcong, New Jersey's largest lake and a major recreational resource.
Mount Arlington was incorporated as a borough by an Act of the New Jersey Legislature on November 3, 1890, from portions of Hanover Township, based on the results of a referendum held two days earlier. Additional territory was acquired from Roxbury Township on July 25, 1891, on May 31, 1893, and on May 31, 1894.
While Mount Arlington is now mostly a suburban residential community, it was once a thriving resort community. In the era before the world wars and the advent of air travel, it was a welcome respite for the residents of nearby New York City and Newark.
Every summer, thousands would arrive by train at Landing Station, and then travel by water taxi across Lake Hopatcong to the area's many large resort hotels to escape the city heat and enjoy the famous "Mount Arlington breeze" which always cooled the summer evenings. There was also a major amusement park, Bertrand Island, which featured a world-famous carousel and roller coaster, which operated until the park was closed in 1983.