Conservation efforts determining the health status of individuals can aid in assessing population health and sustainability. Body condition was determined in 65 free-ranging Eastern box turtles (Terrapene carolina carolina) from four locations in Vermilion County, Illinois, in the months of May, July, and September 2014, 2015, and 2016 using computed tomography (CT). Physical examinations were performed to determine morphometric measurements, and CT scans measured body fat. Twenty-three linear models were constructed to determine which morphometric measurements best correlated to fat content. The top two models of body fat included a relationship between mass and carapace width. Fat increases as both mass and carapace width increase. CT, while impractical for daily use, improved on previous methods of measuring body condition and created a calculation that can be applied broadly to Eastern box turtles. By understanding how measurements of mass and carapace width correlate to body condition, practitioners, researchers, and conservationists can evaluate chelonians with increased confidence in the accuracy of their assessment.