Library of Congress Dun and Bradstreet digital book collection
Online volumes have been expanded to cover most of 1859 to 1879 and 1900 to 1924. These are of value for economic historians and business historians as R.G. Dun & Company, now known as Dun & Bradstreet, was a credit reporting agency that provided ratings on an enterprise’s financial strength and ability to pay back debts.
The website has a key to the rankings. It also has maps of the types of businesses in certain US locations.