A friend helped me with a solution that I could place in my functions.php file:
add_filter( 'pre_get_posts', 'my_pre_get_posts' );
function my_pre_get_posts( $query ) {
if ( is_tax( 'locations' ) && empty( $query->query_vars['suppress_filters'] ) )
$query->set( 'orderby', 'comment_count' );
return $query;
}