Nielsen Wire, a useful and free source of research data, has an interesting article on the 10 U.S. counties with the highest percentage of what they call "young money" - those aged 25-34 earning $100k or more.
The data in the article highlights two trends. First, it illustrates the growing importance of Washington D.C. as an economic center. 16 of the top 50 counties with the highest concentration of the young moneyed are in the Washington D.C. area.
The other cities with a major presence on the list are San Francisco, New York and Chicago. In absolute numbers, New York county has the largest total number of those aged 25-34 making more than $100k (768,000) and San Francisco county is second with 332,000.
The second trend is what the article calls "the densification" of young money in major metropolitan areas. This means young people making $100k or more are increasing found in or near urban centers.
As an aside, I think "densification" is a cool word.