from:
http://www.uscis.gov/i-485
Employment-Based Applications
If you are filing for lawful permanent resident status based on an offer of permanent employment in the United States, you should
your I-485 to:
USCIS Nebraska Service Center
P.O. Box 87485
Lincoln, NE 68501-7485
This includes an employment-based I-485 if you are filing a Form I-140, Petition for Alien Worker, concurrently with
your I-485, or an I-485 filing basedon a pending or an approved Form I-140.