Individuals with Down syndrome (DS) are living longer than they used to. This trend has led to a heightened prevalence of DS-associated Alzheimer’s disease (DS-AD) in the adult DS population. Information about the impacts of longer lives and increased DS-AD prevalence is lacking. This information is needed to inform both investment in research development programs for new treatments for DS-AD and policies related to health care and caregiving for aging adults with DS. To begin addressing the knowledge gap, we developed a multistate population simulation and projection model to study trends in DS-AD and the associated impact on caregiving. The study was funded by the LuMind IDSC Foundation, the Alliance for Aging Research, BrightFocus Foundation, and the National Down Syndrome Society.