Timely emergency department (ED) access is vital for young children under five (U-5) years and adults aged \(\ge \) 85 years. This study assessed the spatial equity of populations at higher risk of delayed emergency care across Greater Melbourne to identify priority areas for intervention. We integrated 2021 mesh-block demographics with the geolocations of 39 public and private EDs. Using Voronoi tessellation, we defined service catchments and employed 15 km straight-line buffers as proxies for a 15-minute ambulance response range. Of 386,663 children U-5 and adults \(\ge \) 85 across 46,608 populated mesh blocks, 92.9% lived within 15 km of an ED, while 27,475 (7.1%) individuals lived outside this effective reach. Underserved residents cluster in three peri-urban corridors: Sunbury–Diggers Rest, Little River–Werribee South, and Whittlesea–Kinglake. Five hospitals account for 35% of the groups with elevated emergency healthcare needs caseload. Low-income areas show \(\sim \) 50% higher odds of being outside the 15 km threshold (9.1% vs 6.0%). Geographic isolation, age-related vulnerability, and socioeconomic disadvantage converge to form critical service gaps. Targeted investments in emergency infrastructure, community paramedicine, and equity-focused urban planning are warranted to ensure prompt, life-saving care for Melbourne’s most at-risk populations.
