Mountainside

County:: Union County
County Seat:: No
Area (mi²):: 3.996
State:: New Jersey

Mountainside is a borough located in Union County, New Jersey. Mountainside has a 2025 population of 6,881. Mountainside is currently declining at a rate of -0.3% annually and its population has decreased by -1.53% since the most recent census, which recorded a population of 6,988 in 2020.

The average household income in Mountainside is $235,424 with a poverty rate of 2.85%.The median age in Mountainside is 48.7 years: 49.7 years for males, and 45.3 years for females.

Demographics

The racial composition of Mountainside includes 75.28% White, 12.33% Asian, and smaller percentages for Black or African American, other race and multiracial populations.

Population by Race

Race	Population	Percentage (of total)
White	5,245	75.28%
Asian	859	12.33%
Two or more races	783	11.24%
Black or African American	77	1.11%
Other race	3	0.04%

Mountainside Marital Status

Married

Widowed

Divorced

Separated

Never Married

Economics and Income Statistics

Mountainside's average per capita income is $104,750. Household income levels show a median of $210,100. The poverty rate stands at 2.85%.

Families: A family includes the owner or renter of the home along with everyone related to them - whether through birth, marriage, or adoption. This includes relatives like spouses, children, parents, siblings, grandparents, and any other family members.

Households: A household includes all the people who occupy a housing unit (such as a house or apartment) as their usual place of residence.

Non Families: A nonfamily household is either someone living alone or when the owner/renter lives with people they aren't related to, like roommates.

Name	Median	Mean
Married Families	$247,888	-
Families	$226,389	$254,559
Households	$210,100	$235,424
Non Families	-	$140,209

$104,750

Average Income

$210,100

Median Household Income

2.85%

Poverty Rate