Mountainside's housing stock is characterized by larger-than-average lots and a strong single-family orientation, sustained by long-standing zoning that limits density. The borough's homes span several decades of construction, from mid-century ranches and split-levels to larger custom and contemporary houses, many set on generously sized, landscaped properties. The leafy, low-density streets and proximity to the Watchung Reservation reinforce a suburban, nature-oriented character. Compared with some neighboring Union County communities, the emphasis is on space and privacy rather than high-density development, which shapes both the housing inventory and the buyers the town tends to attract.

Mountainside is a relatively small, cohesive borough, and its identity is defined less by distinct named neighborhoods than by its setting against the Watchung Reservation. Residential streets spread across the ridge, with many homes enjoying wooded surroundings and larger lots. The area around Deerfield School forms a central, family-oriented focus, while the Route 22 corridor along the borough's edge carries the commercial and commuter functions. Echo Lake Park and the reservation anchor the recreational geography. The overall effect is a continuous suburban landscape of established homes, mature trees, and easy access to open space rather than sharply differentiated districts.

Life in Mountainside revolves around the outdoors and the schools. The Watchung Reservation is a year-round destination for hiking, horseback riding, and nature programs, and Echo Lake Park provides a popular loop for walkers, runners, and cyclists, with pedal boats and fishing in warmer months and skating when it freezes. The borough runs its own community pool and recreation programs centered near Borough Hall. The pace is quiet and suburban, with everyday shopping and dining reached along Route 22 or in the surrounding communities of Westfield, Summit, and Berkeley Heights. Residents enjoy a calm, green environment within commuting range of Manhattan.

Mountainside operates its own public school district for kindergarten through eighth grade, anchored by Deerfield School, giving families a self-contained local elementary and middle school experience. For high school, students attend Governor Livingston High School in neighboring Berkeley Heights through a regional sending relationship. This arrangement, combining a small local K-8 district with a well-regarded regional high school, is a frequently cited reason families choose the borough. The schools, together with the borough's parks and recreation programs, give Mountainside a distinctly family-centered character.

Route 22 is the borough's principal corridor, running along its edge and connecting Mountainside to the wider Union County and North Jersey road network. NJ Transit bus service, including the 114 line from the Route 22 corridor, provides a direct commute into the Port Authority Bus Terminal in Midtown Manhattan in roughly an hour. For rail, commuters use nearby stations in Garwood and Westfield on the Raritan Valley Line. Newark Liberty International Airport is a short drive away, and the borough's position between the Garden State Parkway and Interstate 78 supports access across the region.

Mountainside's recreation is anchored by the Watchung Reservation, more than 2,000 acres of protected forest with miles of hiking and bridle trails, Lake Surprise, and the Watchung Stables for horseback riding. The Trailside Nature and Science Center, located within the borough, offers exhibits, programs, and a planetarium that draw families year-round. Echo Lake Park adds two lakes and a flat, popular walking and cycling loop, plus seasonal boating and fishing. The borough also maintains its own community pool, fitness trail, and lighted sports fields and tennis courts near Borough Hall, giving residents a full range of local recreation options.