Snake Identification - St. Louis, MO
It might be a juvenile lined snake (Tropidoclonion lineatum). The What Snake Is That page for Missouri says they are native. In your photo, I see very faint black stripes with a central tan line, which matches a lined snake. Photos of juveniles seem to be rare though.

Lined snakes grow to about 2 feet long and are non-venomous. According to this natural history page, the only venomous snakes in Missouri are pit vipers (of which 5 are native).