in the richer neighborhoods like Ladue, University City, Clayton, etc most business men wear suits. In other areas they have an option for business casual. Enough business casual that some suit makers like Kuppenheiners went out of business.

I worked for a law firm so I had to wear a suit, sans a jacket at times unless I had a meeting with a lawyer. When no lawyer was around I took off my tie and unbuttoned my collar for a bit to get oxygen to my brain.