The privately owned companion dog is an emerging model in geroscience because it shares the human environment and its risk factors, is affected by many of the same age-related diseases, receives comparable medical care, and has excellent veterinary data available. In addition, the dog is the most phenotypically diverse animal species on the planet and includes breeds that represent hundreds of genetically distinct strains, which makes it an exciting model to research how these phenotypic and genetic differences affect clinical outcomes. A shared environment affecting health outcomes across species is referred to as One Health, and this has interesting implications for using dogs as models and sentinels for human epidemiology, including the study of aging, age-related disease and mortality. We analyzed patient records from three primary care US veterinary hospitals from a rural, suburban and urban environment to identify risk factors determining lifespan in n = 20,970 dogs using Kaplan-Meier and Cox Proportional Hazards models. This showed highly significant effects of weight and, after controlling for weight, spaying, environment, and anatomical features like brachycephaly, as well as a genotype-dependent effect of shortened tails. Our findings regarding body size, sex and spaying reflect previous data, indicating our sample was representative; however, living environments, as well as brachycephalic and tail length status have not previously been described as influencing life span in dogs. In addition to veterinary medicine, our results have interesting implications for human health in these environments under the One Health paradigm.