Where are Processing libraries installed when added from the Sketch menu?

Question

When I add a library in Processing (Sketch > Import Library > Add Library), where is it installed?

Answer 1

They're installed in your sketchbook location.

You can view and change your sketchbook location by going to File > Preferences. The sketchbook location setting is the first option in that dialog:

This sketchbook location is also where your settings are stored, as well as the default place where sketches are saved.

You could have probably figured this out by googling "processing library directory" or by just installing a library and then searching for a directory with that name.