By year: Every year, the Office for Intellectual Freedom (OIF) compiles a list of the Top 10 Most Challenged Books.
By decade: Lists of the 100 most frequently challenged books for 1990-1999, 2000-2009, 2010-2019.
This information is from ALA's "Frequently Challenged Books" webpage.
Banned Books Week YouTube Channel
Top 10 Most Challenged Books of 2019
Top 11 Most Challenged Books of 2018
Top 10 Most Challenged Books of 2017
Top 10 Most Challenged Books of 2016
Top 10 Most Challenged Books of 2015