Illinois 100 is a pretty drive along the Illinois River from Fulton County down to Hardin in Calhoun County, then it follows an even more scenic route along the Mississippi River to Alton.
Intersections from north to south: IL78 at Dunfermine
It joins IL97 south
Then in Lewistown, IL100 follows US24 south as IL97 follows US24 east
US136 joins from the east as US24 goes west, forming a "wrong-way"mulitplex
US24 breaks off and goes west
US136 breaks off and goes east
Next, IL100 joins US67 south as IL103 begins*** (picture is from the south)
IL125 at Beardstown
IL104 joins US67/IL100 near Meredosia
then US67 and IL104 leave to the southeast leaving IL100 without a multiplex
It joins IL106 westbound across the Illinois River***
Then it breaks off and heads south at the tiny town of Detroit
IL108* at Kampsville
IL96 at Kampsville
IL16** at Hardin***
IL16 leaves east
IL3 near Grafton
US67 at Alton.
It passes through these towns: Dunfermine, St. David, Lewistown, Browning, Beardstown, Bluffs, Kampsville, Hardin, Grafton, Elsah, Alton.
*- Technically, IL108 has a tiny stretch in Kampsville. It's about a block long. The fact is that there's a ferry across the Illinois River for travellers on IL108 from Kampsville east. So IL108 runs on this tiny stretch, then the ferry, then on the rest of the road which runs all the way to the
I-55 corridor.
**-IL16's western start point is on the eastern end of the bridge on which IL100 crosses the Illinois River, at Hardin. It follows IL100 from there to about 5 miles southeast of Hardin. Then, it is on its own, spanning almost the entire state to end near Paris.
***-This indicates that there's an Illinois River Crossing between here and the next intersection. There's a total of 3. It starts on the west side of the river, goes to the east side, returns to the west side, and ends on the east side.
