The Pew Research Center has released Book Reading 2016.
Here's an excerpt:
Between 2011 and 2016, the number of Americans who read books on tablet computers has increased nearly fourfold (from 4% to 15%), while the share who read books on smartphones has more than doubled (from 5% to 13%). The share of Americans who read books on desktop or laptop computers has also increased, although by a more modest amount: 11% of Americans now do this, up from 7% in 2011.
By contrast, 8% of Americans now report that they read books using dedicated e-reader devices—nearly identical to the 7% who reported doing so in 2011.