Q:

Magento 2 How to add all country regions in database?

I checked directory_country_region in the database there is no region of the United Kingdom, I need all region of United Kingdom.
Is Magento provide the sheet of all country regions or from where I can add them?
Please help me.

A:

Magento 1: You can use the direct SQL files to add regions into database. For this you can refer this post.
Another way is You can use the Magento custom code to add regions into database. For this you can refer this post.
Also I have found one extension "Regions Manager" that provide facility to add/update regions from backend.  
UPDATE

The solution which I did to add United Kingdom Regions is: I found a
  CSV for united Kingdom states here: Here is the CSV

Just import it in Database and its save my time and effort.

