A US Customs dog named Shadow sniffed out the drugs, which were hidden in four separate shipments in the airport's mailroom.
The packages allegedly came from Laos, a country in Southeast Asia. One of the parcels was invoiced as "Hmong Dresses" and contained 38 pieces of decorative clothes, authorities said.
Chicago Customs and Border Protection officers said they tested the dresses and found them to be saturated with opium.
Other contents were marked as "Traditional Medicines" and contained woodchips, leaves and twigs that also tested positive for opium.
The drugs have a reported street value of almost $500,000, according to Chicago Customs and Border Protection officials.
The parcels were destined for addresses in Minnesota and Wisconsin.