Generally, textbooks and encyclopedias are quickly outdated and are not accepted by most resellers or libraries. Call first.
Other paperback and hard cover books (ie. fiction, history, biography, etc.) may have a long life.
Consider donating to your local library, religious institution for re-sale, or one of the following:
Crusader Thrift Shop
Little Free Library (ask your neighbors; the closest one may not be registered online)
Patriots’ Gateway Retirement home Rockford Rescue Mission Sharestuff
Paperbacks Recycle with regular paper recycling, including at Keep Northern Illinois Beautiful Recycling Center
Hard Cover Books, Text Books
Remove covers and binding, then recycle with regular paper, including at Keep Northern Illinois Beautiful Recycling Center