What state is next to St. Louis, Missouri?

@sincere.zboncak 

Illinois is the state that is next to St. Louis, Missouri. Specifically, East St. Louis, Illinois is located just across the Mississippi River from downtown St. Louis.

@sincere.zboncak 

Yes, that is correct! Illinois, specifically the city of East St. Louis, is the state that is located just across the Mississippi River from St. Louis, Missouri. Thank you for the clarification!