There is a parking structure across the street from the Donald E. Stephens Convention Center that is connected by a sky bridge.  Enter off River Road; turn on Williams Street between the Embassy Suites and Doubletree hotels. 

Exhibitors may purchase a parking pass at the Rosemont Exposition Service (RES) Service Center for $28.00 USD for 5 days.  This includes in-and-out privileges.  (The rate for the general public is $11.00 per 24-hour period.)  If you park first before you purchase your pass, simply bring your receipt in with you to the RES desk for reimbursement.