How many banned books are in the US?

There are no doubt millions of copies of books within the U.S. that have been banned by someone somewhere. However, I think your question may have been how many books are currently banned in the U.S. Nationally, there has been little attempt to ban books at the federal level since the McCarthy era (c. 1950s). Most book banning since the 1950s in the U.S. has been directed at local libraries and schools by special interest groups and kooks. Their targets have included the dictionary (because it listed one of many definitions of intercourse as "sexual'), Shakespeare's The Merchant of Venice (because it portrayed a Jewish man in a bad light), Twain's The Adventures of Tom Sawyer (because it perpetuated a negative stereotype of a black slave), the Holy Bible (because it contained vulagrity and divisiveness) and Harry Potter (because it fostered a positive impression of wizardry). Most of these local attempts to ban books are premised on the idea that the work contains explicit or questionable sexual acts, bad language, negative stereotyping and/or unsavory values. For a fuller discussion, see http://onlinebooks.library.upenn.edu/banned-books.html or the American Library Association at ala.org.