Just to follow up on Mr. Dugan's answer, you want to first of all let SSA know and secondly (as important) DOCUMENT that you have informed SSA. The best way to do so is to send a letter to your local SSA office via certified mail - return receipt requested. You want to keep a copy of your letter and you also want to keep the green card (signed for by an SSA employee) as evidence that you did, in fact, notify SSA of your decision. Again, letting them know is one thing; being able to PROVE that you informed SSA is the more important thing.
Also, just want to remind you that IF things don't work out you may be able to reinstate your SSA benefits - hopefully without having to reapply and start the entire process over. So continue to maintain a file holding all documents relating to your SSA disability. You'd be surprised how useful having those documents might be someday in the future.
Best wishes for success with your new business.
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