If you use US Postal Service, the address is:
USCIS
P.O. Box 805887
Chicago, IL 60680-4120
For courier/express deliveryes:
USCIS
Attn: AOS
131 South Dearborn - 3rd Floor
Chicago, IL 60603-5520
I am sending my package in December, anyone knows what is best to use USPS, FeDex, or UPS...