By city or state?
Based on a 2014 survey about the used kite market, I'd say
#1 market = California
#2 = Oregon
#3 = Florida
I believe Texas, the Carolina's, and the North East regions are strong too.
Since the survey is dated, I'm sure some things have swayed a bit.
My bet is CA is still a leading market. Northern CA alone has 11 kite shops and the most amount of schools listed in the entire US (last check was 16).
http://www.thekiteboarder.com/2014/02/k ... et-trends/
Edit: To add to my statement, CA is also where the following brands are either HQ'ed or their US distribution is HQ'ed...
Ride Engine also has its roots in CA.
Best's US office is located in San Francisco and they just opened up a showroom with Mafia Bags in SF.