I had never wondered how many libraries are in the United States until someone asked me on desk. There don’t seem to be any comprehensive surveys of every type of library, but the ALA has some guidance.
According to their site there are over 120,000 libraries in America.
If you would like to see the breakdown of which types of libraries they looked at, and the relationships between the numbers and branches vs. administrative hubs, please visit: http://www.ala.org/tools/libfactsheets/alalibraryfactsheet01
If you read my post about how book advances work, you’ll know that this is heartening news. If I could get just half of those libraries to buy my book in 2013 I’ll be a happy librarian.