Our research examines whether there is a causal effect between expanding health insurance and diabetes incidence. Comprehensive county‐level data from the United States is used to study the effect of Medicaid expansion on diabetes rates. The analysis is based on cross‐county variation according to Affordable Care Act health care reforms, along with county share‐eligibility variation. Difference‐in‐difference and triple‐difference statistical regression specifications are employed to control for confounding variables. The results suggest a slight negative relationship between expanding health insurance and diabetes diagnoses.