ImportancePrevalences of alopecia areata (AA), alopecia totalis (AT), and alopecia universalis (AU) are poorly established.ObjectiveTo estimate overall and subgroup prevalences of AA and its subtypes.Design, Setting, and ParticipantsThis cross-sectional study using electronic records comprising the Explorys database (Watson Health, IBM Corporation) included children, adolescents, and adults seeking healthcare across the 4 census regions in the US between January 1, 2019, and December 31, 2019. The statistical analysis was conducted between July 21, 2022, and December 22, 2022.Main Outcomes and MeasuresPrevalent cases of AA, AT, and AU.ResultsOf the 1 093 176 patients who met inclusion criteria, 1812 had at least 1 code for AA, 1216 female (67%) and 596 male (33%) patients. Overall age-and-sex standardized prevalences among adults and among children and adolescents were observed to be 0.18% and 0.10%, respectively. The age-standardized prevalence ratio in women to men was 1.32. Standardized prevalence was highest in those aged 30 to 39 (297 per 100 000; 95% CI, 263-335) and 40 to 49 (270 per 100 000; 95% CI, 240-303) years. The highest standardized prevalence was observed among Asian patients (414 per 100 000; 95% CI, 306-548), followed by patients reporting another race or multiple races (314 per 100 000; 95% CI, 266-368), Black (226 per 100 000; 95% CI, 199-255), and Hispanic/Latino (212 per 100 000; 95% CI, 129-328) patients. White patients had the lowest standardized prevalence (168 per 100 000; 95% CI, 157-179) among racial and ethnic subgroups. Relative to White patients, standardized prevalence ratios for Asian, Black, and Hispanic/Latino patients were 2.47 (95% CI, 2.17-2.81), 1.35 (95% CI, 1.26-1.44), and 1.26 (95% CI, 1.03-1.55), respectively. Cases of AT and AU comprised approximately 9% of patients diagnosed with AA.Conclusions and RelevanceThe findings of this cross-sectional study suggest that there is a significant burden of AA, AT, and AU in the US in which people of color, particularly Asian Americans, appear to be disproportionately affected.