Among over 3,000 U.S. counties, the median percent of adults over 18 who had one of five selected underlying conditions (chronic obstructive pulmonary disease (COPD), heart disease, chronic kidney disease, diabetes, and obesity) associated with higher risk of severe illness from COVID-19 was 47% and ranged as high as 66%. Obesity was the most common underlying condition reported at the local level with an estimated median county prevalence of 35.4%, followed by diabetes (12.8%), COPD (8.9%), heart disease (8.6%), and chronic kidney disease (3.4%). This information can be used by state and local decision-makers to help identify populations at higher risk for severe illness from COVID-19 due to underlying medical conditions and guide mitigation efforts, resource allocation, and implementation of public health response strategies. See the full CDC MMWR report here.