Background Dementia among younger people is rapidly emerging as a global health concern; however, comprehensive research on its shifting burden trends remains insufficient. Methods Data on the prevalence, incidence, mortality, and disability-adjusted life years (DALYs) associated with dementia occurring in individuals <70 years were extracted from the Global Burden of Diseases, Injuries, and Risk Factors Study 2021. Average annual percentage changes (AAPCs) were calculated to assess trends in age- specific fi c rates (ASRs), including age-specific fi c prevalence rates (ASPRs), age-specific fi c incidence rates (ASIRs), age- specific fi c mortality rates (ASMRs), and age-specific fi c DALY rates (ASDRs) while young-onset dementia (YOD) burden trends were analyzed. The correlation between ASR/AAPC and the sociodemographic index (SDI) was evaluated. Findings In 2021, the global prevalence of dementia in individuals <70 years increased by 122.33%, with a 128% increase in new cases since 1990. Concurrently, deaths and DALYs of individuals <70 years with dementia rose by 119.28% and 119.77%, respectively. The AAPCs of YOD ASRs during 1990-2021 - 2021 initially increased and then decreased with increasing SDI levels, with the highest AAPCs of ASPR (2.20 [95%CI: 2.08-2.32] - 2.32] per 100,000), ASIR (2.25 [95%CI: 2.06-2.45] - 2.45] per 100,000), ASMR (2.04 [95%CI: 1.93-2.15] - 2.15] per 100,000), and ASDR (2.06 [95%CI: 1.99-2.13] - 2.13] per 100,000) observed in middle-SDI levels. Additionally, females <70 years bore a higher burden of dementia globally, and gender differences are still widening. Interpretation The growth rate of YOD is accelerating, particularly in the middle to high SDI region with females bearing a disproportionately higher burden of YOD. Copyright (c) 2024 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).