I did some research on the original Illinois Central route. I did most of this on the Web, but I also read the book "Main Line of Mid-America", which was printed in 1951 on the 100th anniversary of the founding of the Illinois Central.
Track construction for the original Illinois Central system started in 1852 and was completed in 1856. The line started in Cairo and ran north through Carbondale, Du Quoin, and Centralia. Just North of Centralia it split into two branches, forming a great letter V. The west branch ran through Vandalia, Decatur, Bloomington, Mendota, Dixon, Freeport, and Galena, ending at Dunleith, which was opposite Dubuque on the Mississippi River. This branch did not include Rockford, which was on the Galena and Chicago Union railroad (later merged into the Chicago and Northwestern).
The east branch of the Illinois Central ran north and northeast through Effingham, Matoon, Urbana, Rantoul, Gilman, Kankakee, Calumet, and Chicago. The original IC tracks came into downtown Chicago along the shores of Lake Michigan and the station was at the south end of Grant Park. In 1972 Amtrak rerouted all passenger trains into Union Station. Today, the Illinois Central right of way in Illinois is owned by the Canadian National Railway.
As far as I can tell, the City of New Orleans route in Illinois is exactly the original Illinois Central route from 1856, with the exception of the short passage from Union Station to the shores of Lake Michigan. From that point on, the various stations I will be passing will indeed be the same ones that Abraham Lincoln passed through as he rode the Illinois Central. Many of those stations were built in the middle of nowhere, and the name of the station then became the name of the town.
Here is an excerpt from a letter from John W. Foster, a geologist for the Illinois Central: "In 1853 I traversed the Illinois Central between Chicago and Urbana, a distance of more than 125 miles. It passed through a nearly unbroken prairie, with here and there a house by the margin of a wooded belt. Now [1856] the traveler never loses sight of cultivated farms, and at intervals of at least every ten miles are flourishing villages."
An interesting anecdote from my reading is the story of Grand Crossing, which was originally well outside of Chicago, but is now a neighborhood of city. In the spring of 1852: "At a point on the open prairie a few miles south of Chicago, the Northern Indiana [railroad] and the Illinois Central were to cross. The Northern Indiana, which reached the crossing point ahead of the Illinois Central, flatly denied the latter the right to cross its track at grade. Whereupon Chief Engineer Mason of the Illinois Central sent a crew of husky tracklayers to the scene under cover of darkness, overpowered the guard, and installed the crossing before daybreak. The Northern Indiana protested, but it was no use, the crossing was in and so it remained. This point is now known as Grand Crossing."
Anyway, the early days of the Illinois Central are fascinating. Not only did Lincoln do legal work for the IC, but George B. McClellan was also an executive of the IC in those days. This is the same General McClellan who would later be appointed (and then dismissed) by Lincoln during Civil War. Amazing!