Background: We evaluated the fallout after closure of an urban level 1 trauma center using geospatial methodology to define the Hahnemann University Hospital catchment area, hypothesizing that firearm homicides and prehospital drive time would increase. Methods: A Prais-Winsten interrupted time series analysis utilized firearm assault data from the Philadelphia Police Department before (Jan 2015 to June 2019) and after (July 2019 to Sept 2025) Hahnemann University Hospital's closure. Using geospatial analysis, Hahnemann University Hospital catchment area was defined as the area where the drive time to the Hahnemann University Hospital was shortest. The primary outcome was death, and the secondary outcome was drive time. We used descriptive statistics and performed logistic regression with interrupted time series analysis for death, incorporating injury patterns, patient characteristics, and the absence of Hahnemann University Hospital. Results: A total of 1,457 adult firearm assaults occurred within the Hahnemann University Hospital catchment area: 452 firearm assaults with 94 deaths before closure and 1,005 firearm assaults with 181 deaths after closure. Drive time increased within Hahnemann University Hospital catchment area after closure (10.3 vs 11.3 minutes, P < .001). With P < .200 on univariable analysis, torso gunshot wounds (odds ratio, 0.975; 95% confidence interval, 0.943-1.001; P = .143), multiple gunshot wounds (odds ratio, 1.060; 95% confidence interval, 1.017-1.097; P = .005), and extremity gunshot wounds (odds ratio, 0.970; 95% confidence interval, 0.941-1.010; P = .058) were included in the final model. On multivariable interrupted time series analysis, there was no difference in mortality after Hahnemann University Hospital's closure (beta = -0.186; 95% confidence interval, -0.440 to 0.070; P = .146). Conclusion: Mortality for firearm assault victims within the Hahnemann University Hospital catchment area was unchanged after Hahnemann University Hospital's closure despite increased drive time. While Philadelphia was protected from changes in mortality with hospital clustering, other cities with known trauma deserts or rural areas may not be. (c) 2026 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.