Sir, like the others, believe the '...originally commissioned by the State of Illinois...' to be in error.
The New Orleans, Jackson, and Great Northern Railroad Company was chartered in both Louisiana and Mississippi to build a railroad from New Orleans, La., to Jackson, Miss. It received financial support from both state governments as well as private investors. Commencing construction in 1852, the line was completed to Canton, Miss., in March 1858.
From the description of New Orleans, Jackson, and Great Northern Railroad shipment record, 1870-1873. (Louisiana State University). WorldCat record id: 429047897
'New Orleans, Jackson and Great Northern Railroad Company' is available to read online at...
Also please see -
https://civilwartalk.com/threads/civil-war-railroad-papers.149039/page-2#post-1953034
The IC started to cooperate with, invest in, then acquire, railroads south of the Ohio river post-war.
It is no coincidence that the first efforts to build railroads in Mississippi began in the early 1830s, shortly after the signing of treaties that made Choctaw and Chickasaw land available for settlement and investment by US citizens, because nineteenth-century railroad building was closely...
mississippiencyclopedia.org
Now while not in any official capacity, I can see movers and shakers from Illinois cheering on and supporting any rail ventures from the Gulf that headed north towards the IC from a purely business perspective.
HTHs,
USS ALASKA