There are conventions in every state, it's just a matter of scale. There is an event in Iowa City in September. It won't be something huge like the San Diego event, but you'll still have an opportunity to mingle with some like-minded folks and hopefully meet some cool guests.
Wizard World Comic Con, one of the biggest Con series in the US, has added Des Moines to its 2015 schedule. That one would be quite a bit larger, I expect.