IMPORTANCE: A timely diagnosis is crucial in ensuring high-quality care for individuals with dementia. Comparing age and health status at the time of dementia diagnosis across population subgroups can provide insights into vulnerable groups that may experience delayed diagnosis and/or a poorer prognosis. OBJECTIVE: To examine how age and health at the time of dementia diagnosis vary across sociodemographic subgroups. DESIGN, SETTING, AND PARTICIPANTS: A nationwide cross-sectional study of individuals with an incident dementia diagnosis from either specialist care or who were dispensed antidementia drugs, identified from the Swedish National Patient Register and the Prescribed Drug Register between January 2018 and December 2022. EXPOSURES: Sociodemographic status at the time of dementia diagnosis was assessed through linkage with national registers and included education, place of birth, living arrangement, family status, and family disposable income. MAIN OUTCOMES AND MEASURES: Health status was assessed by calculating the number of dispensed medications during the year preceding dementia diagnosis, as well as the Charlson Comorbidity Index (CCI) and Hospital Frailty Risk Score (HFRS) using specialist diagnoses during the preceding 5 years. RESULTS: Of the 107 707 individuals with a dementia diagnosis, 61 127 (56.8%) were women and the mean (SD) age at diagnosis was 82.0 (7.7) years. Individuals with lower education, living alone or in a care home, or without a close relative were a mean (SD) of 3.1 (7.3) years older when diagnosed with dementia compared with their counterparts. At the time of diagnosis, individuals who had lower than high school education had higher CCI (odds ratio [OR], 1.11
95% CI, 1.07-1.15) and more medications (OR, 1.38
95% CI, 1.33-1.44) compared with those with university education. Age and health status at dementia diagnosis did not differ significantly by place of birth or income. CONCLUSIONS AND RELEVANCE: This nationwide register-based study indicated that clinical diagnosis of dementia may be significantly delayed among individuals with low education, those living alone or in a care home, or those without a close relative. These groups also had poorer health at the time of dementia diagnosis, which may impact their prognosis negatively. Future efforts should focus on improving health services to better address the diagnostic and care needs of these vulnerable subgroups.