Objective We assessed the relationship between county-level prevalence of adult obesity and voting behaviors in the 2016 US presidential election. Methods Spatial autoregressive regression was performed to examine county-level obesity rate in relation to the vote margin for the Republican Party presidential candidate, defined as the percentage difference in votes received by the Republican presidential candidate and those received by the Democratic presidential candidate, adjusting for county sociodemographics and state fixed effects. Results A quadratic association was found between county-level obesity rate and the vote margin for the Republican Party presidential candidate-the margin increased when obesity rate increased from 11.8% to 34.1%, but after reaching its peak of 36.1%, it started to decrease when obesity rate further increased to 47.9%. Conclusion Typically, health disparity has been considered as a political outcome, whereas its impact on political behavior is rarely examined. Our findings indicate obesity disparities may not only be influenced by political decisions but also affect political behavior. Future studies should elucidate the pathway linking obesity to voting behavior and track the long-term trend of this relationship.