The mailing address for Form AR-11, Alien’s Change of Address Card, is indicated on the second page of the form itself. Note that this address is to be used for AR-11 documents only.
Currently, the valid address for sending a duly completed and signed Form AR-11 is the following:
U.S. Department of Homeland Security
Citizenship and Immigration Services
Attn: Change of Address
1344 Pleasants Drive
Harrisonburg, VA 22801
Please also keep in mind that if you use Online Change of Address (egov.uscis.gov/coa/displayCOAForm.do), there is no need to file a paper Form AR-11.