The South Dakota Festival of Books takes place September 20-22. There is an app available which can be found on the website. There are lots of events taking place, some of which require tickets. Some of these ticketed events are free. There will be authors there as well.
The Library of Congress National Book Festival takes place this Saturday and Sunday on the National Mall. There is a children's and teens pavilion as well.
The Brooklyn Book Festival is taking place this weekend, with a large celebration on September 22 at Brooklyn Borough Hall. This festival also has an associated app available for download from the website. There are youth and children events taking place as well.
If you are in the area of any of these festivals, make sure to attend!
