Nonfatal firearm assault incidents are more prevalent than gun homicides, however, little is understood about nonfatal firearm assault incidents due to a lack of accurate data in the United States. This is a descriptive study of all nonfatal firearm assault incidents identified through police and clinical records from 2007 to 2016 in Indianapolis, Indiana. Records were linked at the incident level to demonstrate the overlap and non-overlap of nonfatal firearm assault incidents in police and clinical records and describe differences in demographic characteristics of the victims. Incidents were matched within a 24-h time window of the recorded date of the police incident. Data were analyzed in fall 2020. There were 3797 nonfatal firearm assault incidents identified in police reports and 3131 clinical encounters with an ICD 9/10 diagnosis-based nonfatal firearm-related injury. 62% (n = 2366) of nonfatal firearm assault incidents matched within 24 h to a clinical encounter, 81% (n = 1905) had a firearm related ICD code: 40% (n = 947) were coded as a firearm-related assault, 32% (n = 754) were coded as a firearm-related accident; and 8.6% (n = 198) were coded as undetermined, self-inflicted or law enforcement firearm-related. The other 20% (n = 461) did not have an ICD firearm related diagnosis code. Results indicate most nonfatal firearm assault incidents overlap between police and clinical records systems, however, discrepancies between the systems exist. These findings also demonstrate an undercounting of nonfatal firearm assault incidents when relying on clinical data systems alone and more efforts are needed to link administrative police and clinical data in the study of nonfatal firearm assaults.