This study examined the roles, effectiveness, and spatial distribution of built environment agencies in mitigating building collapse in Lagos State, with the objective of assessing institutional performance, identifying operational gaps, and proposing improvement strategies. The study addressed a gap in empirical assessments that integrate institutional roles with spatial analytics in the context of building collapse management, drawing on institutional theory to explain how regulatory structures influence enforcement outcomes. Using a mixed-methods research design, the study involved a population comprising officers of eleven key built environment agencies and professionals in the construction sector. A sample of 165 respondents was obtained using purposive and stratified sampling techniques to capture agencies directly involved in building control, planning, and emergency response. Data were collected using structured questionnaires, key-informant interviews, and spatial datasets processed through GIS-based tools, including average nearest neighbour and buffer analysis, while quantitative data were analysed using descriptive and inferential statistics. Qualitative responses were analysed thematically to complement the spatial and statistical results. Findings show that agency effectiveness remains moderate, with a mean performance score of 3.02 on a 5-point scale, while GIS results reveal clustering of regulatory activities in Lagos Mainland and Lagos Island, leaving peripheral zones with relatively weak oversight. The study also found that 64% of respondents identified fragmented inter-agency coordination as a major contributor to persistent collapse incidents. The research concludes that improving spatial coverage, strengthening institutional capacity, and enhancing collaborative regulation are essential for reducing building collapse in Lagos State. It is recommended that the State government institutionalise integrated spatial monitoring, increase technical staffing across agencies, and harmonise enforcement frameworks to strengthen the building safety system.