Someone illegally filed my oldest son on their tax return. I have no idea who it could be. How can I find out?

I am by no means an expert but I am assuming you received a letter from the govt stating that you cannot claim him because he was claimed by someone else? Do you have an ex, or parent who might have done this? Is this something completely out of the blue?

If you have a letter from the govt, I would suggest copying it. Then take a copy of your sons birth certificate and social security card and attach them. Write a cover letter to the person who sent you the letter in the first place, stating that you do not know how anyone could claim you son on their return. Suggest there is another child with the same name and social security number might have been confused and reference your attachments. Ask them to do an investigation because their letter has you worried that someone stold your sons identity. Then, send the letter via certified mail. Keep the receipts with all the paperwork and wait for a response. If you do not receive a response within 45 days, I would suggest calling the person on the letter and asking them to please help you clear up this matter.

Hope this helps.