Correction: I counted only 11 major Maker Faires (not dozens), but there are 61 mini-Maker Faires in 2013.
The largest Maker Faire is the original Bay Area event, and they had around 120k people this year.
Here are the cities with major Maker Faires:
Kansas City (KS)
Fort Wayne Regional (IN)
World New York (NYC)
Bay Area (San Mateo, CA)
There are dozens of major Maker Faire events in major cities (Bay Area, New York, Detroit, Rome...) and mini-Maker Faires in smaller cities.
Here's a list of the upcoming Faires:
I count 50 upcoming Faires this year.