Mountainside borough, New Jersey
Official LSAD Designation: Mountainside borough • Census GEOID: 3448510
• Union County
Demographics & Population Profile
Population and demographics for Mountainside borough.
| Demographic Variable | Estimate / Count | Margin of Error | Period | Source |
|---|---|---|---|---|
| Total Population (2025 PEP Estimate) | 7,346 | — | 2025 | Census |
| Median Age | 48 yrs | ±6.2 | 2020-2024 | Census ACS 5-Year 2024 |
| Total Households | 2,508 | ±123 | 2020-2024 | Census ACS 5-Year 2024 |
Source: U.S. Census Bureau (PEP, ACS 5-Year).