There's at least one in every state. Anime Iowa would probably be the closest to you, depending on where in Iowa you live. Nearby, there's also Anime Detour in Minnesota and Anime Nebraskon in... well, Nebraska.
http://animeiowa.com/
http://animedetour.com/
http://www.animenebraskon.com/
I've personally been to all 3, and can say without a doubt they're great beginner cons. Anime Detour was my personal first back in '08.