Community water fluoridation is considered a significant public health achievement of the 20th century. In this paper, the hypothesis that added water fluoridation has contributed to diabetes incidence and prevalence in the United States was investigated. Panel data from publicly available sources was used with population-averaged models to test the associations of added and natural fluoride on the outcomes at the county level in 22 states in the years 2005 and 2010. The findings suggest that a 1 mg increase in the county mean added fluoride significantly positively predicts a 0.23 per 1,000 person increase in age-adjusted diabetes incidence (P < 0.001) and a 0.17% increase in age-adjusted diabetes prevalence percent (P < 0.001), while natural fluoride concentration is significantly protective. For counties using fluorosilicic acid as the chemical additive, both outcomes were lower: by 0.45 per 1,000 persons (P < 0.001) and 0.33% (P < 0.001), respectively. These findings are adjusted for county-level and time-varying changes in per capita tap water consumption, poverty, year, population density, age-adjusted obesity and physical inactivity and mean number of years since water fluoridation started. Sensitivity analyses revealed robust effects for both types of fluoride. Community water fluoridation is associated with epidemiological outcomes for diabetes."