ORD is currently the fastest growing (big) airport in the world with 9.8% in passenger growth through May. The fastest growing (big) airport last year was Seoul Incheon at 9.6%. May itself saw an 10% increase over the previous year. This has been fueled primarily by domestic growth, which is up 11.08% YTD with international up 1.55% YTD.
http://www.flychicago.com/SiteCollection...0Traffic%20Data/0515%20ORD%20SUMMARY.pdf