WooCommerce, by default, only recognizes countries/regions which are listed in the ISO 3166 standard. The body who determines valid countries is a trusted and reliable source and it has been the stance of the development team to use this list as the “source of truth”. This does tend to cause problems for example, if a shop owner is shipping from a place such as Northern Ireland. Given that the ISO standard considers Northern Ireland as part of the UK. This has the potential to confuse customers into thinking that shipping is not available to Northern Ireland if that is where they are shipping to as well as adding an extra burden to the shop manager when setting up shipping zones.
Thankfully, WooCommerce does provide a filter that can be used to customization this behaviour. Below is an example of how Northern Ireland to the shipping zone configuration:
This also requires one more snippet to bring everything together:
And the result in the configuration:
Not sure what to do with code snippets? See What Do I Do With These Code Snippets?