Q: Can you suggest the most effective way to post multiple-locations jobs without creating duplicates?
A: I would recommend picking one location and mention all other locations in job description (for example: "Locations: New York, NY, Seattle, WA, Denver, CO").You may change main location from time to time, or post job descriptions for different locations (and include all locations into every job descriptions).
Q:If you are trying to post to all states and the cities within do you have to place ads to all the cities within the states to have them posted in that area?
Do you have a mass posting for states and their cities so you do not post so many?
Or when you post does it go automatically through out the US?
A: All your job posting are available to everyone. If job seeker does not specify the location -- she would find your posting.But if job seeker is looking specifically for some location -- then she wouldn't find your job posting (unless locations match).
Note, that duplicate postings are perceived as spam by job seekers.
I recommend to make only single job posting (to avoid duplicates), but include all locations in job description (so if candidate searches for specific location -- she would find your posting).
Think about what your potential employees are looking for.
If they would not specify any location criteria in their search -- don't bother with location at all.
If they would search for jobs in their states -- put these states in your job posting.
If they search for jobs in their metro areas -- put specific metro-areas in your job posting.