Seeking routing suggestions for Big Rivers ride in Southern Illinois. My tentative route:

Start in Carbondale.
South on EITHER Route 127 or Route 3 to Cairo (which is better?)
Ride along Ohio River (Routes 37/45) to Metropolis
Ride along Ohio River north (Routes 146/1) via Cave in Rock Park to Golconda, Shawneetown

Return to Carbondale via Route 13 or any better local roads to the north of it

This is from the 1969 American Youth Hostel Atlas! 

Seeking scenic, low-volume roads. Any alternatives/suggestions would be welcome. Also any general sense of terrain

You might want to have a  look at the Tunnel Hill State Rail Trail.

https://dnr.illinois.gov/parks/park.tunnelhill.html

I pedaled a portion of that trail one day when pedaling a circular route from Vienna to Cairo to Cape Girardeau.

I enjoyed pedaling the Cave in Rock to Golconda to Vienna route, but can't compare it to other nearby routes. The old river towns are very interesting.

The terrain tends to be relentlessly hilly when not following a river or the rail trail.

Highly recommend adding the Tunnel Hill Trail. Rode most of it last fall. Excellent riding. 

My knowledge is from the mid 1980s, so more current than 1969 but still rather dated.

Highway 13 is a busy 4 lane highway, at least between Marion and Carbondale.  The roads around Crab Orchard Lake are much better for cycling.

The ACA TransAm route passes through Carbondale and Cave in Rock and may be suitable.

I'm on the road right now, will check when I am back home next week to see what else I see.

Some of the county roads in that region are loose gravel so some review would be in order before committing to them.

The Trail of Tears is also in that area and may be of interest.

In keeping with your Big Rivers theme, I strongly recommend going a couple miles south of Cairo to Fort Defiance State Park. The southernmost tip of Illinois, where the blue Ohio river flows into the brown Mississippi river.

My 2014 Steel City to Cow Town tour didn't follow rivers very much, but it took me to the arbitrary beginning and end of the Ohio river. The Ohio river arbitrarily begins in downtown Pittsburgh, where the Allegheny and Monongahela rivers merge. 

The Ohio river arbitrarily ends where it flows into the Mississippi river, even though the Ohio river has the larger flow.

As promised now that I'm back home in front of my computer, have a look at this.  Note that I've done little more than open Ride With GPS and toss in the start point, and the towns you mentioned you wanted to visit or pass through.

https://ridewithgps.com/routes/44618430

I make no guarantees as to suitability or reliability.  Use or ignore at your own discretion and risk.

This is awesome! I downloaded it to my phone. A cue sheet, elevation profile, ascent/descent analysis - the modern way to travel! I need to do this for all of my future rides. 

Glad you approve!  A couple notes:

I forgot to include Metropolis explicitly but RWGPS may have put it in.  I also missed Shawneetown.

You'll want to review the entire route carefully before setting off.

The terrain is rolling to somewhat hilly, as you'll have noted from the RWGPS profile.  Take careful note of the vertical scale, though: it can seriously exaggerate what is really easy terrain, and vice versa. 

You'll need a paid RWGPS subscription to navigate the route from the app.  The free version lets you display it but cash is needed for real time navigation.   I don't know whether the free version supports downloading routes in GPS file format, but if it does you might be able to go that route (so to speak).

That part of the state is quite rural and intermingles farms and wooded patches.  Small roads are sometimes unpaved, so a review with aerial or street view is recommended before committing. 

Good luck, and I hope you enjoy the journey! 

Hi again Phil

I've created another variation of the route, to include Metropolis, Shawneetown, and a few other places.  This route is longer and therefore more ambitious than the first one I drew; not sure how much time you're planning to spend, what your lodging / accommodation intentions are, etc.

https://ridewithgps.com/routes/44625206

I chose the start/end point more carefully than just "Carbondale"; Phoenix Cycles is (or was, 40 years ago) a very good bike shop.  The Bike Surgeon, a block or two south, has changed hands since I was there and I know nothing of the current owner's policies, skills, etc. but "back in the day" it was a very interesting place, and catered specifically to the needs of touring cyclists.

I camped in the Ridgway City Park in 2017; for $5 it's a deal that's hard to beat.  There's not much else in town- a convenience store / small grocery, and a few other businesses were there in 2017 but I haven't been back since COVID so I don't know how many survived.

El Dorado's a bit larger and may have more to offer.

Harrisburg's bigger yet; after that you'll pass through some very very small hamlets but nothing much until you're back in Carbondale.

Any town or city I've routed you through may (or may not) have additional resources (bars, gas stations, cafes, etc.) but I haven't really made an effort to find them for you or to put them on the route.

As before, a cautious review of the route and due diligence are advised before you set off!

Deviations I'm making from the route you mapped are (1) to take Illinois 3 - not 127 via Anna - to Cairo: this puts on extra miles but avoids (I'm told) some of the hills I can see from the ride profile - gonna split this into two days by staying in Cape Girandeau Missouri (I should have listed that as a stop point);  I ran the 3 vs 127 option by some bike shops (including Phoenix!); they gave a thumbs up to 3 narrowly (2) gonna do a straight shot on US 13 from Harrisburg back to Carbondale. What's the advantage of the route you mapped- seems indirect?  More scenic? I'm told 13 has a shoulder.

Re the bike shops, I spoke with both big bike stores in Carbondale - Phoenix and Carbondale Cycle. Bike Surgeon is a going concern but yes run by different folk and no longer in Carbondale.

Curious as to what was the start and end points on your trip in 2017.