Chicago (ZAU) Air Route Traffic Control Center
From The RadioReference Wiki
The Chicago ARTCC (ZAU) started at Midway Airport in the late 1950's. As the need for increased personnel and equipment arose, Aurora, Illinois was selected for the new operating location for ZAU. The building was completed in a period of 5 years and personnel transitioned into the new facility in 1962.
ZAU is a level 12 facility providing service to the Chicago and Milwaukee Metropolitan area and 16 underlying approach control facilities. The center's 9 areas of specialization are comprised of 24 high altitude sectors and 24 low altitude sectors.