Just an FYI - There will not be a 5150 in St. Louis this year

In May there is an Oly race at Lake Carlyle, usually around the 18th......well run race, but not a large field.....maybe 200-250.  It's an hour away.

It's the Gateway Triathlon put on by 3discipline racing.  They also run an OLY race at Carlyle in the Fall but I don't know much about it.

In August there is the Lake St. Louis triathlon, also Oly distance...... it's a well established race and also well run. Put on by Ultramax.  Also a field of 200-250.

There is a nice triathlon in St. Charles in June.....not quite Olympic distance but close.(1000M swim, 20 mile bike, 4 mile run) That race is put on by Big Shark and they do open water swim practice on Sundays starting in March at the race site.

Each race is USAT certified if that's important to you, but the last I heard 3discipline racing may be cutting ties with USAT.

There's also the Octomax (sprint) and Quartermax (Oly) at Innsbrook in late June.  The 5150 actually took the place of these races last year but this year it's going back to the Octomax/Quartermax.  There's also the Halfmax Championship the same day at Innsbrook - if you're looking for HIM distance.  They're run by Ultramax sports. 

The Rec-Plex in St Peters also does races in June and Sept that are not quite Oly distance.  Swim is 500, bike is 21 miles and the run is about 4.4 miles. 

I just got this information today if you are interested in a HIM in St. Louis area.  This will be a very fast course.....and very cool on the Mississippi River road for most of the bike.

http://racemaker.org/borderwarstri/