From the code in `/wp-includes/widgets.php` for the `WP_Category_Widget` class we have the following code *(line 438 in WordPress v3.0.4):*

    $cat_args = array('orderby' => 'name', 'show_count' => $c, 'hierarchical' => $h);
    if ( $d ) {
      $cat_args['show_option_none'] = __('Select Category');
  
    wp_dropdown_categories(
      apply_filters('widget_categories_dropdown_args',$cat_args)
    );

From that I would surmise that the hook `'widget_categories_dropdown_args'` would allow you to set an `'orderby'` parameter?





P.S. Have you ever considered using *(something like)* [PhpStorm][1]? As you ask lots of *"How can I get access to..."* kind of questions so you'd probably find yourself an order of magnitude more productive if you had a tool like PhpStorm that could quickly get you these answers. Just a thought...


  [1]: http://www.jetbrains.com/phpstorm/