<b><i>Introduction:</i></b> Thailand is a rapidly aging society. The percentage of older adults with diabetes has also been increasing. Since diabetes mellitus is documented as a risk factor for dementia, it is important to address cognitive impairment in older adults with diabetes. Thus, this study aimed to evaluate the prevalence and associated factors of cognitive impairment among older adults with diabetes in a suburban primary health center in Thailand. <b><i>Methods:</i></b> A cross-sectional study in 244 diabetic patients aged 60 years or older was conducted in a primary health care unit in Pathum Thani, Thailand. Cognitive function was assessed with the validated Thai version of the Mini-Addenbrooke’s Cognitive Examination Test. Sociodemographic and health characteristic data were obtained. <b><i>Results:</i></b> The prevalence of cognitive impairment was 54.5% (133 out of 244). Multivariate logistic regression disclosed that factors significantly associated with cognitive impairment were ages 70–79 years compared to ages 60–69 years (odds ratio [OR] 1.90, 95% confidence interval [CI]: 1.01–3.62, <i>p</i> value 0.048), ages ≥80 years compared to ages 60–69 years (OR 3.65, 95% CI: 1.19–11.24, <i>p</i> value 0.024), education ≤ primary school (OR 7.28, 95% CI: 3.56–14.89, <i>p</i> value &#x3c;0.001), and medication managed by caregiver compared to self-management of medication (OR 13.40, 95% CI: 1.55–116.10, <i>p</i> value 0.019). <b><i>Conclusion:</i></b> We revealed that approximately half of older adults with diabetes had cognitive impairment. This finding strongly suggests the need to include cognitive assessment in a standard clinical practice guideline for diabetic patients and to focus more on individuals who are very old, have low education, or are unable to manage their drugs by themselves.