Googlebooks contains a scan of an 1873 Congressional Act "Revising and embodying all the Laws authorizing Post-Roads, in force on the first day of December, one thousand eight hundred and seventy-three." To be frank, I stumbled upon it while looking for something totally unrelated. That's often how the best things are found.
The title pages have been reproduced as a part of this blog post. The specific publication also included legislation related to the District of Columbia.
The page numbering starts over again for the legislation related to the Post-Roads (a direct link to the first page is here).
The Act begins with bridges over the Mississippi River...
And continues with a list of post roads listed alphabetically by state. The page reproduced here (48) lists roads for part of Illinois.
Even a few post offices at individual residences are listed.
Too bad there are no maps, but this was a really interesting find.
Give it a look for those areas where you have an interest.
