Mountainside is a borough in Union County, in the U.S. state of New Jersey. The borough is located on a ridge in northern-central New Jersey, within the Raritan Valley and Rahway Valley regions in the New York metropolitan area. As of the 2020 United States census, the borough's population was 7,020, an increase of 335 (+5.0%) from the 2010 census count of 6,685, which in turn reflected an increase of 83 (+1.3%) from the 6,602 counted in the 2000 census.Table 7. Population for the Counties and Municipalities in New Jersey: 1990, 2000 and 2010, New Jersey Department of Labor and Workforce Development, February 2011. Accessed May 1, 2023.
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.Snyder, John P. The Story of New Jersey's Civil Boundaries: 1606-1968, Bureau of Geology and Topography; Trenton, New Jersey; 1969. p. 239. Accessed May 30, 2024.
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."Best Places To Live - The Complete Top Towns List 1-100" , New Jersey Monthly, February 21, 2008. Accessed February 24, 2008.
History In 1958, part of Nike missile battery (NY-73) was installed, with the missile launchers themselves in Mountainside while the radar station was installed in Berkeley Heights. It remained in operation until 1963. Remnants of the control site are located adjacent to Governor Livingston High School, while the part of Watchung Reservation that was cleared in order to accommodate the missile launchers became the Watchung Stables.Harpster, Frank. "Missiles in Mountainside — Nike Battery NY-73", from The Hetfield House of the Mountainside Historic Preservation Committee, November 2009. Accessed June 17, 2015. "Nike NY-73 had two parts. The launcher was in Mountainside at the entrance from Summit Lane.... The second part was located in Berkeley Heights on the hilltop next to Governor Livingston High School – this was the Missile Tracking Radar Station."
Geography
According to the United States Census Bureau, the borough had a total area of 4.04 square miles (10.47 km2), including 4.00 square miles (10.35 km2) of land and 0.05 square miles (0.12 km2) of water (1.11%).
Mountainside is bordered by the Union County municipalities of Summit to the north, by Springfield Township to the east, by Westfield to the south and by Berkeley Heights and Scotch Plains to the west.Areas touching Mountainside, MapIt. Accessed March 1, 2020.Union County Municipal Profiles, Union County, New Jersey. Accessed March 1, 2020.New Jersey Municipal Boundaries, New Jersey Department of Transportation. Accessed November 15, 2019.
Demographics
Racial and ethnic composition +Mountainside borough, New Jersey – Racial and ethnic compositionRace / Ethnicity (NH = Non-Hispanic)Pop 2000Pop 2010Pop 2020% 2000% 2010% 2020White alone (NH)6,1115,7545,49892.56%86.07%78.32%Black or African American alone (NH)611211340.92%1.81%1.91%Native American or Alaska Native alone (NH)6020.09%0.00%0.03%Asian alone (NH)1803234662.73%4.83%6.64%Native Hawaiian or Pacific Islander alone (NH)4000.06%0.00%0.00%Other race alone (NH)17500.02%0.10%0.71%Mixed race or Multiracial (NH)40732030.61%1.09%2.89%Hispanic or Latino (any race)1994076673.01%6.09%9.50%Total6,6026,6857,020 100.00%100.00%100.00%
2020 census
As of the 2020 census, Mountainside had a population of 7,020. The median age was 46.6 years. 22.3% of residents were under the age of 18 and 22.9% of residents were 65 years of age or older. For every 100 females there were 97.1 males, and for every 100 females age 18 and over there were 92.8 males age 18 and over.
100.0% of residents lived in urban areas, while 0.0% lived in rural areas.
There were 2,399 households in Mountainside, of which 35.8% had children under the age of 18 living in them. Of all households, 71.8% were married-couple households, 7.0% were households with a male householder and no spouse or partner present, and 18.1% were households with a female householder and no spouse or partner present. About 15.7% of all households were made up of individuals and 11.1% had someone living alone who was 65 years of age or older.
There were 2,564 housing units, of which 6.4% were vacant. The homeowner vacancy rate was 2.0% and the rental vacancy rate was 21.3%.
2010 census
The 2010 United States census counted 6,685 people, 2,468 households, and 1,866 families in the borough. The population density was . There were 2,558 housing units at an average density of . The racial makeup was 91.31% (6,104) White, 1.97% (132) Black or African American, 0.00% (0) Native American, 4.94% (330) Asian, 0.00% (0) Pacific Islander, 0.42% (28) from other races, and 1.36% (91) from two or more races. Hispanic or Latino of any race were 6.09% (407) of the population.
Of the 2,468 households, 30.8% had children under the age of 18; 66.7% were married couples living together; 6.5% had a female householder with no husband present and 24.4% were non-families. Of all households, 21.6% were made up of individuals and 15.6% had someone living alone who was 65 years of age or older. The average household size was 2.64 and the average family size was 3.10.
23.2% of the population were under the age of 18, 4.8% from 18 to 24, 18.2% from 25 to 44, 30.0% from 45 to 64, and 23.7% who were 65 years of age or older. The median age was 47.2 years. For every 100 females, the population had 92.7 males. For every 100 females ages 18 and older there were 88.1 males.
The Census Bureau's 2006–2010 American Community Survey showed that (in 2010 inflation-adjusted dollars) median household income was $116,210 (with a margin of error of +/− $22,182) and the median family income was $135,086 (+/− $14,679). Males had a median income of $95,030 (+/− $9,312) versus $58,818 (+/− $8,974) for females. The per capita income for the borough was $52,844 (+/− $5,530). About 1.5% of families and 3.5% of the population were below the poverty line, including 3.1% of those under age 18 and 8.1% of those age 65 or over.DP03: Selected Economic Characteristics from the 2006-2010 American Community Survey 5-Year Estimates for Mountainside borough, Union County, New Jersey , United States Census Bureau. Accessed July 17, 2012.
2000 census As of the 2000 United States census there were 6,602 people, 2,434 households, and 1,925 families residing in the borough. The population density was . There were 2,478 housing units at an average density of . The racial makeup of the borough was 95.09% White, 0.94% African American, 0.09% Native American, 2.80% Asian, 0.06% Pacific Islander, 0.27% from other races, and 0.74% from two or more races. Hispanic or Latino of any race were 3.01% of the population.Census 2000 Profiles of Demographic / Social / Economic / Housing Characteristics for Mountainside borough, New Jersey , United States Census Bureau. Accessed July 17, 2012.DP-1: Profile of General Demographic Characteristics: 2000 - Census 2000 Summary File 1 (SF 1) 100-Percent Data for Mountainside borough, Union County, New Jersey , United States Census Bureau. Accessed July 17, 2012.
There were 2,434 households, out of which 29.3% had children under the age of 18 living with them, 71.9% were married couples living together, 5.3% had a female householder with no husband present, and 20.9% were non-families. 17.9% of all households were made up of individuals, and 11.9% had someone living alone who was 65 years of age or older. The average household size was 2.60 and the average family size was 2.95.
In the borough the population was spread out, with 21.1% under the age of 18, 3.8% from 18 to 24, 22.9% from 25 to 44, 27.3% from 45 to 64, and 24.9% who were 65 years of age or older. The median age was 46 years. For every 100 females, there were 89.2 males. For every 100 females age 18 and over, there were 87.1 males.
The median income for a household in the borough was $97,195, and the median income for a family was $105,773. Males had a median income of $78,595 versus $52,667 for females. The per capita income for the borough was $47,474. About 2.0% of families and 3.0% of the population were below the poverty line, including 1.9% of those under age 18 and 2.9% of those age 65 or over. Government
Local government Mountainside is governed by a Mayor-Council form of government as authorized through the Option Municipal Charter Law (commonly called the Faulkner Act). The township is one of 71 municipalities (of the 564) statewide that use this form of government.Inventory of Municipal Forms of Government in New Jersey, Rutgers University Center for Government Studies, July 1, 2011. Accessed June 1, 2023. The governing body is comprised of the mayor and the six-member borough council. Under this form of local government, the mayor is elected for a term of four years and there borough council members are elected for three-year terms, with two seats coming up for election each year in a three-year cycle. Both the mayor and Borough Council are elected at-large, that is, to represent the entire community. Elections for all officials in Mountainside are conducted on a partisan basis during the November General Election.2012 New Jersey Legislative District Data Book, Rutgers University Edward J. Bloustein School of Planning and Public Policy, March 2013, p. 94. Shows form of government as Borough."Forms of Municipal Government in New Jersey", p. 10. Rutgers University Center for Government Studies. Accessed June 1, 2023.
, the mayor of Mountainside is Republican Paul N. Mirabelli, whose term of office ends on December 31, 2027. Members of the Borough Council are René Dierkes (R, 2028), Steven Matejek (R, 2026), Donna Pacifico (R, 2028), Donald Rinaldo Jr. (R, 2027), Alex Van Deusen (R, 2027), and Valerie Wass (R, 2026).Borough Council, Borough of Mountainside. Accessed January 20, 2026. "Mountainside is governed by a Mayor and Council form of government, as authorized through the Option Municipal Charter Law (Faulkner Act). Enacted by the State Legislature in 1950, this form of local New Jersey government provides for the election of a Mayor for a term of four years and a Borough Council of varied complement. In our case, the Borough Council consists of six members, elected for staggered three year terms. Both the Mayor and Borough Council are elected at-large, that is, to represent the entire community."Union County Elected Officials, Union County, New Jersey Clerk. Accessed January 20, 2026.General Election November 4, 2025 Official Results, Union County, New Jersey, updated December 5, 2025. Accessed January 20, 2026.General Election November 5, 2024 Official Results, Union County, New Jersey, updated November 22, 2024. Accessed January 9, 2025.General Election November 7, 2023 Official Results, Union County, New Jersey, updated November 22, 2023. Accessed February 19, 2024.
Federal, state and county representation Mountainside is located in the 7th Congressional DistrictPlan Components Report, New Jersey Redistricting Commission, December 23, 2011. Accessed February 1, 2020. and is part of New Jersey's 21st state legislative district.Municipalities Sorted by 2011-2020 Legislative District, New Jersey Department of State. Accessed February 1, 2020.2019 New Jersey Citizen's Guide to Government, New Jersey League of Women Voters. Accessed October 30, 2019.Districts by Number for 2011-2020, New Jersey Legislature. Accessed January 6, 2013.
Politics