In our woocommerce instance we have added custom checkout fields for invocing (identification number of entity and its tax number) via

add_filter( ‘woocommerce_checkout_fields’ , ‘custom_override_checkout_fields’ );

function custom_override_checkout_fields( $fields ) {
$fields[‘billing’][‘billing_ico’] = array(
‘label’ => __(‘IČ’, ‘woocommerce’),
‘placeholder’ => _x(‘IČ’, ‘placeholder’, ‘woocommerce’),
‘required’ => false,
‘class’ => array(‘form-row-first’),
‘clear’ => false
);
}

However from time to time we find “Select a County” in the saved value. I have found the value in shipping-calculator.php, however I was not able to find how this value gets into the database…

Any ideas where to look?

Read more here:: Woocommerce Custom Checkout field saving bogus from time to time