IMPORTANCE: Although Black women are known to have higher hypertension rates than White women, longitudinal investigations of racial disparities in early hypertension onset and the role of neighborhood factors in shaping these differences are severely limited. OBJECTIVE: To quantify racial disparities in early hypertension onset among women and examine the degree to which these disparities vary across levels of neighborhood socioeconomic disinvestment. DESIGN, SETTING, AND PARTICIPANTS: This study used data from women participating in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study, a national longitudinal cohort study. Participants were recruited between 2003 and 2007. Data analyses were carried out from January to August 2025. EXPOSURES: Self-reported race and ethnicity and level of neighborhood (ie, census-tract) socioeconomic disinvestment (low, moderate, or high), determined using a summary score of 6 socioeconomic indicators from US Census Bureau data. MAIN OUTCOMES AND MEASURES: The primary outcome was age of hypertension onset, which was based on age at self-reported physician diagnosis or measured high blood pressure (≥140 mm/Hg systolic or ≥90 mm/Hg diastolic). Weibull accelerated failure time models with age as the time scale were used to estimate racial differences in age of hypertension onset, accounting for left, interval, and right censoring. Estimates were adjusted for individual-level sociodemographic characteristics and health-related factors. Models evaluating disparities across neighborhood disinvestment additionally accounted for neighborhood clustering and rurality. RESULTS: There were 15 313 women included in the study (mean [SD] age at baseline, 64 [9.5] years), of which 7079 (46.2%) self-identified as Black and 8234 (53.8%) self-identified as White. Black women acquired hypertension a median of 9.6 (95% CI, 9.0 to 10.2) years earlier than White women, independent of sociodemographic factors. Inequities persisted across levels of neighborhood disinvestment. In neighborhoods with low disinvestment Black women had hypertension a median of 9.2 (8.2 to 10.3) years earlier than White women. Within highly disinvested neighborhoods, hypertension occurred a median of 8.0 (95% CI, 6.9 to 9.1) years earlier in Black than White women. CONCLUSIONS AND RELEVANCE: In this cohort study, earlier hypertension onset experienced by Black compared with White women persisted regardless of neighborhood context, even after controlling for a wide range of covariates.