Reasons for decline remain uncertain.
Offsetting projections of an increase, researchers have found that the rate of dementia among the U.S. population has declined by 12% in the last 24 years, according to The New York Times in "U.S. Dementia Rates Are Dropping Even as Population Ages."
While this is good news, the reasons for the decline are not known.
There is some evidence to suggest that people are seeking treatment for diseases such as diabetes and high blood pressure more often which has contributed to the decline in dementia. Other evidence suggests that increasing overall educational levels in the U.S. has been a contributing factor. However, that might be nothing more than a correlation.
If researchers can figure out why the rate of dementia is in decline, it will help them to understand the disease and to develop preventative measures.
Of course, despite the decline in the rate as the population continues to age, the total number of people in the country with dementia is actually increasing. It would be a bad idea to assume you will not eventually suffer from it and neglect to get powers of attorney drawn up, just in case.
An estate planning attorney can advise you on your best course of action.
Reference: New York Times (Nov. 21, 2016) "U.S. Dementia Rates Are Dropping Even as Population Ages."