Last Pay Check not received

What is the name of your state? N.J.
I was working for an internet company for 2 1/2 years as a moderator and was fired on July 16, They stated "job performance" as the reason though my performance hadn't changed, I believe they had other unprovable motives, regardless. Now I am waiting for my last check and I know for fact current employees have received theirs. My question is how long do I wait to take action. (Previous checks took 2 days)It is 9 days past due. I have written to my former boss and she said it was mailed on the 20th.(I'm not sure I believe this with the way I was let go)The company is based in NY city. What do I do to collect? I was a dedicated and faithfull contractor.

In NJ the final paycheck is due the next scheduled regular payday. Since she claims it has already been mailed, my suggestion would be that you call back and POLITELY ask them to please double check because you have not received it. Suggest POLITELY that they either trace the check (if it was sent by a service that provides tracing) or that they stop payment and reissue. Do not in any way infer that you do not believe that they actually mailed it, even if you don't. You catch a lot more flies with honey than with vinegar.

If they refuse to cooperate, then, still politely, advise them that in that case you will have no option but to ask the Department of Labor for assistance in collecting your last check. If that still doesn't shake it loose, do contact the DOL.

Thank You I appreciate your answer. I did request a land mail address of the accounting dept. and the name of someone to contact. As all of the positions are held by people around the country.
There really isn't anyone in particular that I can find on my own to request a reissue of the check. Will time run out on me eventually where I would not get what is owed for time worked? Does it matter that the company is NY and I'm in NJ should I contact NY DOL?

No, since you are in NJ, NJ regs apply. The time to file a complaint will run out on you, yes, but it's not going to happen in the immediate future - I'm not sure how long you have but it's considerably longer than a month. If you haven't been able to locate someone to request a reissue from in another week or so, file a complaint then. You'll be in more than enough time.