On Demand Javascript Coding

The reference page is [login to view URL] I would like the large [login to view URL] to load on demand instead of with the page load. I would like it to load the county data when the user clicks on the map. It is my hope that this will speed up the initial page load time as this .js file is over 50k. Also make the default message inside the town selections (on the left) say "Choose County Above" plus, of course, continue to allow the drop down menu to have the same functionality as clicking the map.. any questions? Please ask.. I'd prefer working with someone who is familiar with this technique and can take care of it quickly. Should be real fast for someone familiar. Thank you.