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//Create Custom Checkout Field
add_filter( 'woocommerce_checkout_fields' , 'custom_checkout_field' );

function custom_checkout_field( $fields ) {
//See Cacher DB "Woo Checkout Fields & Arrays" for a full list of field options
\!h     $fields['__shipping__']['__custom-field__'] = array(
\!h        'label'     => __('__Field Label__', 'woocommerce'),
\!h    'placeholder'   => _x('__Placeholder Text__', 'placeholder', 'woocommerce'),
    'required'  => false,
    'class'     => array('form-row-wide'),
    'clear'     => true
     );

     return $fields;
}

//Display field value on the order edit page
add_action( 'woocommerce_admin_order_data_after_shipping_address', 'my_custom_checkout_field_display_admin_order_meta', 10, 1 );

function my_custom_checkout_field_display_admin_order_meta($order){
\!h    echo '<p><strong>'.__('__Form Field Title__').':</strong> ' . get_post_meta( $order->get_id(), '___custom-field__', true ) . '</p>';