I can confirm that if I launch OneNote from my Start menu and go to File | Options | Save & Backup it shows my OneNote desktop app is configured to save my notebooks to my local C:\Users\\ folder by default.
I can confirm that if I launch OneNote from my Start menu and go to File | Options | Save & Backup it shows my OneNote desktop app is configured to save my notebooks to my local C:\Users\\ folder by default.