Chicago to St. Louis

[DonRotolo]

If you take the train (a reasonable option) you then have the disadvantage to not having transport around St Louis, thus limited to the local subway or walking. With a charter bus you also have a way around town if desired. AMTRAK is a quasi-private (meaning Government-subsidized but needs to try to make a profit) entity, and they are good but train travel is possibly the least desirable transit option in the USA.

Between those two cities, as many have noted, there isn't much but farmland.

I would at least inquire the cost from ORD to STL by air; it may be less than expected.