Removed: the county’s 1970s-era mainframe, moved to read-only in March 2026 and retired; and its remaining AS/400 midrange systems, retired in 2025.
Outcome: a stated saving of $6.5 million a year from the mainframe, and another $483,000 a year from the AS/400 systems.
In March 2026 Cook County, Illinois moved its 1970s-era mainframe to read-only and said in July that full decommissioning was expected by the end of that month. Those figures measure cost rather than incidents; the security argument is the simpler one, that each retired machine stops needing patches, audits, an owner and an exception.
The board president set the goal in 2010 and it took sixteen years to reach, which is the part worth planning for: the last handful of users is what keeps a zombie alive.
Source: Cook County, Cook County Named Top 10 Digital County for Seventh Straight Year, Earns National AI 50 Award (29 July 2026)