Illinois Bell is the name of the Bell Operating Company serving Illinois.

Their headquarters are at 225 West Randolph St., Chicago, IL. After the 1984 Bell System Divestiture, Illinois Bell became a part of Ameritech, one of the 7 original Regional Bell Operating Companies. The Illinois Bell name continued to be used until January 1993, when Ameritech dropped all of their individual Bell Operating Company names in favor of using their corporate name, Ameritech, for marketing purposes. In 2002, SBC dropped the Ameritech name in favor of "SBC" as a national brand. On January 1, 2003, Illinois Bell, for regulatory business, was renamed Illinois Bell Telephone Company d/b/a SBC Illinois.

Illinois Bell, in 1971, became the first ever telephone company to offer Call waiting, Three-Way Calling, Speed Calling, and Call forwarding, all popular telephone service options to this day.

Illinois Bell's legal name was changed again in 2006, following conclusion of SBC Communications' purchase of AT&T, to Illinois Bell Telephone Company d/b/a AT&T Illinois. After being held by AT&T (pre-1984), Ameritech, and SBC, as of 2005, they are now part of the "new" AT&T.

AT&T | Bell System | Public utilities of the United States | Telecommunications companies of the United States | Telecommunications companies | 1920 establishments