Abstract Background and Aims The 2024 European Society of Cardiology (ESC) guidelines introduced ‘elevated blood pressure’ [systolic blood pressure (SBP) 120–139 mmHg or diastolic blood pressure (DBP) 70–89 mmHg] as a new category positioned between non-elevated blood pressure (BP) and hypertension. The dementia risk associated with this reclassification remains unclear. Methods A nationwide Korean cohort of 2.8 million adults aged ≥40 years who underwent health screening in 2009 was analysed. Participants with prior dementia or dementia diagnosed within 1 year after cohort entry were excluded. Blood pressure was classified as non-elevated BP, elevated BP, or hypertension according to the 2024 ESC definitions. Incident dementia—including Alzheimer’s disease (AD) dementia, vascular dementia (VaD), and all-cause dementia—was tracked until 2018. Cox proportional hazards models were used to estimate adjusted hazard ratios (aHRs). Results During a mean follow-up of 8.1 years, 121 223 dementia cases occurred. Compared with the non-elevated BP group, dementia risk was modestly increased in the elevated BP group [aHR 1.016; 95% confidence interval (CI) 0.996–1.037] and significantly higher in the hypertension group (aHR 1.029; 95% CI 1.006–1.051). The associations were particularly pronounced for VaD (elevated BP: aHR 1.159; hypertension: aHR 1.372), whereas they were not significant for AD dementia. These associations were more pronounced among midlife adults and women. Conclusions Based on the 2024 ESC BP classification, both elevated BP and hypertension were associated with an increased risk of dementia, especially VaD. These findings support the clinical relevance of 2024 ESC criteria and highlight midlife adults and women as potential priority targets for early BP management to preserve cognitive health.