Here's a nice map from a reddit user showing current STL Metrolink lines and in-the-works extensions:
Image Source:
https://www.reddit.com/r/StLouis/comments/11gortk/comment/japujrt/
The extension from Shiloh Scott AFB to MidAmerica Airport (more cornfield miles on the far right) is fully funded by Illinois and under construction. The City North-South extension (yellow line) is in the environmental review stage and should begin construction in 2-3 years.
But, yeah, about 1/3+ of the system is currently wasted on IL cornfields and IL/MO low-density suburbs because politics.