This small extension adds region to NPCs.
Region can be filtered on, and there's a region group view.
The By Type and Details list views have a region column added.
This extension is not locked or vaulted. You're free to open it, adjust it, add more fields, whatever you like.
I included comments in the code to help you figure out how it works.
If you do alter it, create a copy with a different name so your hard work is not overwritten when this extension is updated.