In a statewide survey, dementia was found in 3% of adults age 40+; 6%, age 60+; and 12%, age 80+. Among adults with Down syndrome, the rates were 22% for adults age 40+ and 56% for adults age 60+. Observed onset occurred in the mid-60s (early 50s for those with Down syndrome). Alzheimer-type dementia was the most frequent diagnosis. With the occurrence of dementia expected to rise proportionately with the increase of longevity among adults with intellectual disabilities, care systems will have to raise the "index of suspicion" among staff and families, become "dementia capable," and improve their diagnostic and technical resources, as well as their care management supports designed to prolong the "aging in place" of adults affected by dementia.