In October 2005, Florida relaxed restrictions on the use of lethal force in self-defense with the Florida stand your ground law (SYG). We examined whether and how the impact of the Florida SYG varied based on the demographic and economic conditions of each of its counties. Using data from the Florida Universal Crime Reports on homicides and firearm homicides from 1999 to 2014, we found that the impact differed significantly by county urbanization, unemployment, and pre-law homicide rates. The largest increases in homicide and firearm homicide occurred in proportionally safer, richer, and less ethnically diverse suburban counties. These findings reveal that the law may have had the opposite effect than intended, and more strongly impacted counties considered safe, suburban and economically successful.