woocommerce/docs/code-snippets/add-a-country.md

post_title
Add a country

Add this code to your child theme’s functions.php file or via a plugin that allows custom functions to be added, such as the Code Snippets plugin. Avoid adding custom code directly to your parent theme’s functions.php file, as this will be wiped entirely when you update the theme.

if ( ! function_exists( 'YOUR_PREFIX_add_country_to_countries_list' ) ) {
  /**
   * Add a country to countries list
   * 
   * @param array $countries Existing country list.
   * @return array $countries Modified country list.
   */
  function YOUR_PREFIX_add_country_to_countries_list( $countries ) {
    $new_countries = array(
      'NIRE'  => __( 'Northern Ireland', 'YOUR-TEXTDOMAIN' ),
    );

    return array_merge( $countries, $new_countries );
  }
  add_filter( 'woocommerce_countries',  'YOUR_PREFIX_add_country_to_countries_list' );
}

if ( ! function_exists( 'YOUR_PREFIX_add_country_to_continents_list' ) ) {
  /**
   * Add a country to continents list
   * 
   * @param array $continents Existing continents list.
   * @return array $continents Modified continents list.
   */
  function YOUR_PREFIX_add_country_to_continents_list( $continents ) {
    $continents['EU']['countries'][] = 'NIRE';

    return $continents;
  }
  add_filter( 'woocommerce_continents', 'YOUR_PREFIX_add_country_to_continents_list' );
}