If available, see below for a list of known police frequencies for Mountainside, New Jersey. Or, navigate to another city or town within Union County, to view the local police frequencies.
| Elizabeth | Fanwood | Garwood | Kenilworth | |
| Linden | Mountainside | New Providence | Plainfield | |
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| Rahway | Roselle | Roselle Park | Summit | |
| Westfield | ||||
Detect police activity and stay ticket-free in Mountainside, New Jersey with these police radar detectors.