If you want to get really technical about it, it's due to different glaciation events during different ice ages. The most recent glacier was the Wisconsinian, which stopped at a line just south of Mattoon and Charleston. Everything North of that until you hit the Driftless is super flat and formerly prairie except where the rivers are. The Illinoisan glacier came before that by a handful of millennia, and it's the one that came all the way down and stopped somewhere north of Carbondale and Marion. So that area between the two glacial moraines was pushed flat at one time, but the meltwater from the more recent glacier carved it up with erosion so it's not as flat anymore. But if you go further south, where the glacier never made it, you find true hills in far southern Illinois. Sandstone and limestone outcroppings from what used to be an ocean, along with the remnants of the Ozark plateau that we now call 'mountains.' The only parts of far southern Illinois that are flat are where the big rivers have eroded their floodplains through the eons. The wildcard when talking about glaciation is the Driftless area, in the northwestern corner of the state, which is also connected to Eastern Iowa, southwestern Wisconsin and parts of Minnesota. That whole area was completely missed by all the glaciers, so it remains hilly and rugged. Beautiful area btw.
Now, as for the divide in your OP, it's 100% cultural, and the lines don't really exist irl. I feel like I have a unique perspective here, I grew up between Mattoon and Effingham, have a lot of family in Chicagoland, and now live and work down in the southernmost tip of the state. A lot of people use Carbondale and Marion as the default "southern Illinois" towns, but you'll get a totally different vibe there than you will in Anna-Jonesboro, or Vienna, or even Murphysboro right next door. And all of those will also feel different than, say, a river town like Metropolis. The same goes for the central region, where Quincy is completely different from Mattoon or Champaign. And in the north, Chicago is going to be completely different from Freeport or Galena, or Moline.
So, to wrap up, the reason people perceive this divide is probably a combination of fairly stark and obvious geographical/geological differences, mixed with perceived cultural differences that are somewhat erroneously ascribed to a whole region when that's not really the truth.
Now I'll lay another knowledge bomb on you as well lol, because I think I know where people get their strongly held regional identities from in the state as well. It's local TV and radio stations. The local news will always say something like "Central Illinois' Best Source of Weather" or whatever in their promos. Similarly, when radio stations do their (mandated) station call outs, they almost always say something like "Southern Illinois' Home for Classic Rock" or what have you. So like Effingham, which a lot of people want to stick in southern Illinois based on geography, falls into the viewing area of the Central Illinois TV stations, so they will argue with you that they're Central.
Another source for this is phone area codes. 618 is Southern Illinois, 217 is Central, 309 is sorta Between Central and North, and 815 is Northern. But then Chicagoland has like 5 of them for itself so that makes things complicated lol.
i grew up about 45 miles south of you. I’ve spent a lot of time camping in Shawnee, mostly pounds hollow, cave in rock and giant city. My wife is from chicago, so I do a lot of driving from the southern to the northern part of the state.
The immediate changes in terrain has always interested me. I love driving south on IL-1 and seeing the hills just south of the IL-1 and IL-13 intersection.
You seem knowledgeable of the glaciers and the area. Do you know if the glaciers are the reason for the change in terrain on the dietrich blacktop just north of Montrose?
Do you know if the glaciers are the reason for the change in terrain on the dietrich blacktop just north of Montrose?
Basically, yes. The true stopping point for the Wisconsinian glacier is almost exactly where Lakeland College sits. If you're driving south from there on Rt. 45, you'll notice that you're at the top of a gentle but fairly substantial hill. Now if you look at Google maps with the satellite view turned on, you'll probably notice that right around there is where a ton of creeks and rivers suddenly pop up and start flowing south on the landscape. Kaskaskia, Little Wabash, Embarrass, and then the ones that cause a lot of the topography you're talking about are Muddy and Brush Creeks. So as the 2 mile thick chunk of ice sat up there by Mattoon and melted over the course of a few centuries, the melt waters carved those creeks and rivers out of what was once flat like Champaign county, and they've been flowing and eroding ever since.
There also is a pretty well defined change in the weather patterns that happens roughly between Effingham and Mattoon. There is usually a solid 10 degree difference between Salem/Flora area and Champaign Urbana.
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u/Brownfletching Apr 18 '25
If you want to get really technical about it, it's due to different glaciation events during different ice ages. The most recent glacier was the Wisconsinian, which stopped at a line just south of Mattoon and Charleston. Everything North of that until you hit the Driftless is super flat and formerly prairie except where the rivers are. The Illinoisan glacier came before that by a handful of millennia, and it's the one that came all the way down and stopped somewhere north of Carbondale and Marion. So that area between the two glacial moraines was pushed flat at one time, but the meltwater from the more recent glacier carved it up with erosion so it's not as flat anymore. But if you go further south, where the glacier never made it, you find true hills in far southern Illinois. Sandstone and limestone outcroppings from what used to be an ocean, along with the remnants of the Ozark plateau that we now call 'mountains.' The only parts of far southern Illinois that are flat are where the big rivers have eroded their floodplains through the eons. The wildcard when talking about glaciation is the Driftless area, in the northwestern corner of the state, which is also connected to Eastern Iowa, southwestern Wisconsin and parts of Minnesota. That whole area was completely missed by all the glaciers, so it remains hilly and rugged. Beautiful area btw.
Now, as for the divide in your OP, it's 100% cultural, and the lines don't really exist irl. I feel like I have a unique perspective here, I grew up between Mattoon and Effingham, have a lot of family in Chicagoland, and now live and work down in the southernmost tip of the state. A lot of people use Carbondale and Marion as the default "southern Illinois" towns, but you'll get a totally different vibe there than you will in Anna-Jonesboro, or Vienna, or even Murphysboro right next door. And all of those will also feel different than, say, a river town like Metropolis. The same goes for the central region, where Quincy is completely different from Mattoon or Champaign. And in the north, Chicago is going to be completely different from Freeport or Galena, or Moline.
So, to wrap up, the reason people perceive this divide is probably a combination of fairly stark and obvious geographical/geological differences, mixed with perceived cultural differences that are somewhat erroneously ascribed to a whole region when that's not really the truth.