CODE EXAMPLE FOR PHP

woocommerce set default shipping country

add_filter( 'default_checkout_billing_country', 'change_default_checkout_country_and_state' );
add_filter( 'default_checkout_shipping_country', 'change_default_checkout_country_and_state' );
function change_default_checkout_country_and_state( $default ) {
    return 'IT';
}