Sidebar limiting to 10 posts?

Your problem is that you’re using query_posts(), when you need to be using WP_Query(). To display all posts (by ignoring pagination, use the posts_per_page parameter:

$cat_query_args = array(
    // Include posts from category with ID $cat_id
    'cat' => $cat_id,
    // Include all posts
    'posts_per_page' => -1
);

$cat_query = new WP_Query( $cat_query_args );

if ( $cat_query->have_posts() ) : 

     ?>
     <div id="sidebar">
        <h3><?php echo get_cat_name($cat_id); $theCount = 0; ?></h3>
        <ul class="info-list">

        <?php
        while ( $cat_query->have_posts() ) : $cat_query->the_post();

            $theCount += 1; echo 'debug>' . $theCount; 
            ?>
            <li <?php if ($post_id == get_the_ID()) {echo 'class="active"';} ?>>
                <a href="https://wordpress.stackexchange.com/questions/74082/<?php the_permalink(); ?>">
                    <span><?php the_title(); ?></span>
                </a>
            </li>
           <?php

    endwhile; 
    ?>

         </ul>
     </div>
    <?php

endif;

// Be kind; rewind
wp_reset_postdata();