Most of the large cities in the US already have a lot of information available, either guidebooks,DVDs or TV programmes like Billy Connolly's Route 66. For the less well known,to me,places like Wyoming,South Dakota and Utah, I have found that the visitor's centers for the above states where very good at sending information by post.(I would rather have a paper copy than looking online,if possible.)
Always allow plenty of time,before your trip,for the information to be sent. Wyoming,and some others,have offices in the UK,which means the information arrives quicker.
I am going on the Chicago to New Orleans trip,in November,having been to Chicago and St Louis before, I requested information from Memphis and New Orleans.I received a brochure from Memphis within a week and New Orleans within two.Although it is not in New Orleans,their brochure included details of the Oak Alley Plantation,one of the excursions.
Amazon sell a book by Richard Knight called The Blues Highway,which does the same journey from New Orleans to Chicago,but.as the chapters are on a state by state basis,it is easy to find what you want.