Chicago might be a decent place because it's (relatively) close to being in the middle of the country, making it a compromise location rather than having folks from one coast travel all the way to the other coast.
It has lots of decent stuff to do and see there, for those who don't want to be just holed up at a convention the whole time.
It's also close to Canada. Or at least, "not far" in the way that some other places (Atlanta, Orlando, Los Angeles) would be.
Someone brought up Youmacon in Detroit, but that happens too late in the year (cold), so that should be right off the table as an option.
Colossalcon in Sandusky might be good, but consideration must be given to the fact that Sandusky has a small airport and attendees would need to fly into either Cleveland or Toledo, and then somehow arrange transportation all the rest of the way to Sandusky.
For reference, it's an hour-long drive from either city (airport). The only difference is whether you're traveling east or west.