Zitat

The Showmen's League of America was founded in 1913, by a group of outdoor showmen meeting at the Saratoga Hotel in Chicago. Buffalo Bill Cody, the Wild West performer, was elected the club's first president. The Showmen's League of America is the oldest organization of its type in North America.
The Showmen's League promotes friendship and fellowship between its members and the outdoor amusement industry, and pledges to assist those in need through one of its many programs.

taken from showmensleague.org

Chicago seems to be the central place for the US amusement industry. What's the reason for that?

Maybe I'm wrong with this perception, but the name Chicago often crosses my reading.

Buffalo Bill and his fellows met in Chicago.
The Ferris Wheel was erected in Chicago first.
The showman's league has its address in Chicago.
In the movie "rollercoaster" the top five park managers meet in a hotel in Chicago to find out that they are being blackmailed.

Chicago seems to be an important town for doing business, also in the park- and funfair-business.

Another organization that cares for the carnival business:
the OABA Outdoor Amusements Business Association
oaba.org