It is common for major cities to develop along rivers, especially an area where two rivers meet. For a while in the US, the quickest and safest way to head west was along rivers. The Ohio River offered an accessible rout from the 13 original colonies (Penn and VA) to the Northwest Territory and areas gained through the Louisiana purchase.
A number of major cities developed along the Ohio. Including, Pittsburgh, Cincinnati, Louisville. Smaller "secondary cities" developed as well, including a number in present day West Virginia, Kentucky, and Indiana. However, Illinois has no major cities along the Ohio.
The lack of a major city in Illinois is interesting as the Ohio meets the Mississippi in the state. The town of Cairo, Ill is where the confluence is. Today, the town has a population of about 3k. At is peak, it had a population of about 14k. Why didnt it turn into a major metropolitan city?
The Ohio River allows easy access for shipping people and goods to the Mississippi. From the Mississippi, you can head north to the Missouri River (giving you access to the Great Plains) or south to New Orleans (access to the Gulf of Mexico). Cairo, should have been a place for industry, supplies, hotels, and everything else a major transportation hub traditionally has been. The confluence of the Ohio and Mississippi should logically be home to a massive city, like St. Louis. But it isnt. Why?
This question comes up pretty often! Check out u/amp1212's answer from a couple of years ago: Why is there no large settlement at the junction of the Mississippi and Ohio Rivers in the US?
Basically, it floods, a lot, and often.
Hey there,
Just to let you know, your question is fine, and we're letting it stand. However, you should be aware that questions framed as 'Why didn't X do Y' relatively often don't get an answer that meets our standards (in our experience as moderators). There are a few reasons for this. Firstly, it often can be difficult to prove the counterfactual: historians know much more about what happened than what might have happened. Secondly, 'why didn't X do Y' questions are sometimes phrased in an ahistorical way. It's worth remembering that people in the past couldn't see into the future, and they generally didn't have all the information we now have about their situations; things that look obvious now didn't necessarily look that way at the time.
If you end up not getting a response after a day or two, consider asking a new question focusing instead on why what happened did happen (rather than why what didn't happen didn't happen) - this kind of question is more likely to get a response in our experience. Hope this helps!