Higher residential densities are fundamental to creating sustainable, liveable and healthy neighbourhoods; however, community resistance to densification remains a barrier to infill development. We examined the relationship between residential density and the anticipated benefits and (feared) harms that trigger opposition using longitudinal data collected from mid-age adults (n = 3028) in Brisbane, Australia (2007–2016). Participants completed a questionnaire and objective measures were generated for each individual's 1 km buffer at each timepoint. Longitudinal fixed-effects models examined associations between change in density and change in: (1) objective measures of the built environment and crime; and (2) residents' neighbourhood perceptions controlling for time-varying and time-invariant factors, stratified by distance to the central business district (CBD). Dwellings/ha increased, on average, by 1.5 dwellings (p < 0.001), however density levels and the magnitude of change differed by distance to the CBD. Different relationships were apparent depending on distance to the CBD, however despite some exceptions, as densities increased participants' neighbourhoods typically changed in ways that made them objectively more walkable, and subjectively more socially connected, pleasing places to live. The study provides empirical evidence that will help governments and developers communicate the benefits of density and pre-empt or mitigate potential problems that infill developments impose on local communities.