Choropleth map of U.S. counties showing the share of Medicare recipients highly likely to have Alzheimer's disease or related dementias, from January 2020 data. Overall, about 7.1% of Medicare recipients may have dementia. Counties in the South had a much higher prevalence than counties in the Mountain West. In Starr County, Texas, nearly 17% of Medicare beneficiaries may have dementia, the highest rate by county.