If you are mailing your return to the IRS, you should have a "filing instructions" page that printed out most likely as the first page before your return. It will have your IRS filing address.
If you do not see it you can mail your return to the IRS at the following address (if you live in Washington state):
If you ARE NOT enclosing a payment, mail to
Department of the Treasury
Internal Revenue Service
Fresno, CA 93888-0002
If you ARE enclosing a payment use this address:
Internal Revenue Service
P.O. Box 7704
San Francisco, CA
94120-7704
