Winter in the Midwest brings days below freezing. Depending on how North you are in the region — the number of days in a row and how far below freezing varies.
St. Louis is far enough South that you should not trust the ice. (Except for purposely flooded skating rinks.) No matter how smooth and secure it may look — the depth and strength with vary. Is it firmly attached to the shore? Does this pond or lake have open water in another area?
There are animals however, which will ignore this human advice and walk, rest, and sleep on ice unable to support the smallest human.