Zero books are banned by name in the USA. Certain content is: Classified documents (although this is just illegal to share as the one with the original clearance, not to publish/read/possess after), child abuse material, and copyright violations all come to mind.

The majority of "banned books" are books that a random school district/religious school in a conservative part of the country elected not to include in their library at some point. Many of them are required reading in many other school districts and some of the most well known books of the 20th century.

The closer-to-banned ones are generally not included on banned-book-reading-lists and are banned on major retail platforms and long out of print and tend to be racist and/or genuinely subversive to liberal democratic principles. Most of these tend to be some of the most-downloaded-books-on-the-internet, and are also in no way illegal to own in the US - though possession of many is illegal in much of the EU.

An interesting case is United States vs Progressive inc [0] in which the US dropped a lawsuit to prevent a magazine from publishing a how-to guide on building an H bomb and Defense Distributed vs United States Department of State [1] in which the US federal government settled and allowed for the publishing of 3d printed gun files online, previously prevented under arms exports claims.

0: https://en.wikipedia.org/wiki/United_States_v._Progressive,_.... 1: https://en.wikipedia.org/wiki/Defense_Distributed_v._United_...