I live in St. Louis and know quite a few costumers and cosplayers. There are a few cosplay clubs in the area, including StL AMPro or StL Cosplay Freaks (both names seem to be passed around). They're probably the most active. If you're more into the costuming part of cosplay (or just love to appreciate good costumes), there's always the St. Louis Costumers Guild.
Cons 2014 - Ahn!Con | Kawa Kon | Wizard World St. Louis | Costume-Con | Marcon | Cosplacon | Dragon*Con | Archon | Chicago TARDIS
In Progress- Cecil from Welcome to Night Vale
| Jonathan Strange from Jonathan Strange & Mr Norrell
| Madeline Westen from Burn Notice
Misha's Costumes in Progress- Mr Norrell from Jonathan Strange & Mr Norrell
Kawa Kon: Into Darkness in 2014!