what is the address to send your federal tax return?
Depends on where you live and on whether you are getting a refund or owe tax due.
https://www.irs.gov/filing/where-to-file-paper-tax-returns-with-or-without-a-payment
Go to this IRS website for the mailing address, by state, with and without a tax payment - https://www.irs.gov/filing/where-to-file-paper-tax-returns-with-or-without-a-payment