2013 Ranking by Wealth-X reveals Top 10 Cities as far as individuals worth $30 Million.
North America took 5 of the Top 10 spots. I'm pretty certain this is by Metro Area.
North American Cities(and world rank) by the Number of Individuals
Worth $30 Million+, 2013
1 New York 8,025
4 Los Angeles 4,945
5 San Francisco 4,840
9 Mexico City 2,695
10 Washington DC 2,675
World