Where is a newly created library stored in CodeIgniter structure?

It should be placed in application/libraries folder.

In CodeIgniter, a newly created library is typically stored in the application/libraries directory within your project structure. This directory is where custom libraries should reside. By default, CodeIgniter looks for libraries in this directory when they are loaded. So, placing your newly created library in this directory ensures that it can be autoloaded or loaded when needed within your CodeIgniter application.