Mountainside Map
Mountainside is a borough in Union County, New Jersey, United States. As of the 2010 United States Census, the borough population was 6,685.
Mountainside was incorporated as a borough on September 25, 1895, from portions of Westfield Township, based on the results of a referendum held the previous day.
New Jersey Monthly magazine ranked Mountainside as its 16th best place to live in its 2008 rankings of the "Best Places To Live" in New Jersey, as well as eighth in the 2010 list.
Nearby cities include Westfield, Fords, Newark, Morristown, Roseland.