Objective To investigate associations between combinations of insulin resistance (IR) and body mass index (BMI) categories and the risk of diabetes mellitus in a rural population of Korea. Methods This CMC study is an ongoing community-based prospective cohort study. A total of 4,948 subjects age 40 and older, free of T2DM, and had complete data at baseline were included in the present study. According to IR/BMI status, they were classified as normal weight (BMI < 23 kg/㎡) without IR (homeostasis model assessment-IR in the highest quartile, n = 1,578), normal weight with IR (n = 215), overweight (BMI 23- < 25 kg/㎡) without IR (n = 959), overweight with IR (n = 267), obese (BMI ≥ 25 kg/㎡) without IR (n = 1,173), and obese with IR (n = 756). We investigated the associations between BMI/IR categories at baseline and diabetes incidence. Results Four hundred and ninety-six incident cases of diabetes for average of 4.5 years were identified. Multiple logistic regression analysis showed that increased risks for diabetes incidence were observed in the normal weight with IR (odds ratio [95% confidence intervals], 1.88 [1.14-3.07]), overweight without IR (1.71 [1.25-2.32]), overweight with IR (2.41 [1.58-3.69]), obese without IR (1.59 [1.17-2.16]), and obese with IR (4.17 [3.10-6.61]) groups compared with the normal weight without IR group. Conclusion Subjects with combined effect of IR and BMI were at increased risk for diabetes and each factor independently predicted increased diabetes risk. To decrease risk of diabetes, it is necessary that identification of subjects with overweight, obese and/or IR, and an appropriate intervention for each group in the community.