Identifying subgroups of the population with different reasons for uncontrolled blood pressure (BP) can inform where to direct interventions to increase hypertension control. We determined characteristics associated with not being aware of having hypertension and being aware but not treated with antihypertensive medication among US adults with uncontrolled BP using the 2015 to 2018 National Health and Nutrition Examination Surveys (N=2282). Among US adults with uncontrolled BP, systolic BP ≥140 mm Hg or diastolic BP ≥90 mm Hg, 38.0% were not aware they had hypertension, 15.6% were aware but not treated and 46.4% were aware and treated with antihypertensive medication. After multivariable adjustment, US adults who were 18-39 versus ≥70 years old were more likely (prevalence ratio, 1.49 [95% CI, 1.11-1.99]) and those who had a health care visit in the past year were less likely (prevalence ratio, 0.61 [95% CI, 0.48-0.77]) to be unaware they had hypertension. Among US adults with uncontrolled BP who were aware they had hypertension, those 18 to 39, 40 to 49, 50 to 59, and 60 to 69 versus ≥70 years old were more likely to not be treated versus being treated with antihypertensive medication. Not being treated with antihypertensive medication versus being treated and having uncontrolled BP was less common among those with versus without a usual source of health care (prevalence ratio, 0.69 [95% CI, 0.51-0.94]) and who reported having versus not having a health care visit in past year (prevalence ratio, 0.46 [95% CI, 0.35-0.61]). In conclusion, to increase BP control, interventions should be directed towards populations in which hypertension awareness is low and uncontrolled BP is common despite antihypertensive medication use.