A fire at Illinois Bell's Hinsdale Central Office triggers an extended 1AESS network outage once considered to be the "worst telecommunications disaster in US telephone industry history".

Illinois Bell Telephone Company, LLC is the Bell Operating Company serving Illinois. It is owned by AT&T through AT&T Teleholdings, formerly Ameritech.

The Number One Electronic Switching System (1ESS) was the first large-scale stored program control (SPC) telephone exchange or electronic switching system in the Bell System. It was manufactured by Western Electric and first placed into service in Succasunna, New Jersey, in May 1965. The switching fabric was composed of a reed relay matrix controlled by wire spring relays which in turn were controlled by a central processing unit (CPU).