Purpose The burden of diabetes in Mongolia has risen tremendously over the last three decades, and an individually tracked, national registry of diabetes is lacking. Therefore, we aim to investigate diabetes prevalence in Mongolia and analyze some associated factors. Materials and Methods A cross-sectional, nationally representative, population-based survey was carried out in Mongolia. We recruited participants from randomly selected six different clusters for the required 3113 ± 311 sample size. We collected detailed demographics, diabetes condition and medications, anthropometric measurements, body composition, and glucose profiles. Oral glucose tolerance tests were used to diagnose diabetes using the International Diabetes Federation algorithm. Chi-square and multinomial logistic regression tests were used to determine associated factors. Age-standardized prevalence rates were estimated. Results We recruited 3272 participants in the study between June and October 2019. Crude prevalence rates for prediabetes and diabetes were 10.8% (95% CI; 9.8–11.9) and 11.2% (95% CI; 10.1–12.3), respectively. Sixty-one adults were newly diagnosed with diabetes. Age-standardized prediabetes and diabetes prevalence rates were 9.8% (95% CI; 8.5–11.1) and 10.0% (95% CI; 8.7–11.3) among adults 30 or older. Higher BMI, central obesity, diabetes inheritance, sedentary habitus, and hypertension are significantly associated with diabetes in adjusted analysis for sex and age group. Conclusion The prevalence of diabetes has increased at least threefold since 1999 in Mongolia. In addition, numerous modifiable risk factors were associated with diabetes. Therefore, future investigations and programs should focus on combating obesity and sedentary lifestyles and propose dietary recommendations in the context of expanding diabetes in Mongolia.