To determine the association between diabetes status, glycemia, and cognitive function among a national U.S. sample of older adults in the 2011–2014 National Health and Nutrition Examinations Surveys. Among 1,552 adults age ≥ 60 years, linear and multivariable logistic regressions were used to determine the association between diabetes status (diabetes, prediabetes, normoglycemia) and cognitive function Consortium to Establish a Registry for Alzheimer’s Disease-Word Learning (CERAD W-L), Animal Fluency test, Digit Symbol Substitution Test (DSST). Overall, diabetes was associated with mild cognitive dysfunction. In age-adjusted models, adults with diabetes had significantly poorer performance on the delayed and total word recalls (CERAD W-L) compared to those with normoglycemia (5.8 vs. 6.8 words; p = 0.002 and 24.5 vs. 27.6 words; p < 0.001, respectively); the association was non-significant after adjusting for cardiovascular disease. Among all adults, cognitive function scores decreased with increasing HbA1c for all assessments, but remained significant in the fully adjusted model for the Animal Fluency and DSST beta coefficient = -0.44;-1.11, p < 0.05, respectively. As measured by the DSST, the proportion with cognitive impairment was significantly higher for older adults with HbA1c ≥ 8.0% (≥64 mmol/mol) vs. HbA1c < 7.0% (<53 mmol/mol) (14.6% vs. 6.3%, p = 0.04). Dysglycemia, as measured by HbA1c, was associated with poorer executive function and processing speed.