Where do you mail federal tax returns?

This depends on what state you live in. Since you did not say what state you live in I will tell you where to get this information. If you want to clarify where you live I can give you the address if you like. If you wish to look it up yourself you can go to the IRS website at irs.gov and look under forms and publications. Enter form 1040 and pull up the instructions for this form and the addresses are listed at the end of the instructions. There are at least twelve different addresses as there are different ones if you owe or if you are due a refund for each group of states.