Well in an alternate reality Cairo has a population of over 1 Million and St. Louis is a Milwaukee to it’s Chicago.
Heh... I think if Cairo had managed to grow beyond 15,000, it’s not very likely to have gone much higher (short of it becoming a very densely packed city). Remember that it is hemmed in on 3 sides by the river on a very narrow peninsula and it can only grow northward. On either side of it is Kentucky & Missouri, and that’s mostly flat farmland on the MO side (KY has some hills). Culturally, though, it has more in common with Mississippi than Illinois (or even KY, for that matter). It’s closer to MS than Springfield (and it’s only 3 hours from Nashville, making us the closest state capital to it). Still, it is astonishing given its premier location that it has been allowed to decay and fester as it has.