The SSN in question is correct. I have also seen his mothers tax form for 2016 and he is NOT claimed on her form 1099.

[tryan61369]

How do I find out who filed claiming him?

[IreneS · Accepted solution]

UPDATED FOR TAX YEAR 2019

Even though the child's mother may not be claiming him as a dependent, is the child's name and SSN listed on her return?  (for example, for Head of Household filing status)  If so, you will have to print and mail your return.

 If you are sure the number you have entered is correct, and the child's mother did not enter his name/SSN at all on her return, contact the IRS at 1-800-829-1040 for further guidance.