The original egregious violations here - setting off warning bells - (and clearly illegal according to Illinois law, according to SOS Giannoulias) had to do with Texas law enforcement attempting to track out of state abortions.
https://www.nprillinois.org/illinois/2025-06-12/illinois-license-plate-cameras-used-illegally-by-out-of-state-police-giannoulias-says
correction, note: Article says that system had been accessed (without specifying legality) for purposes of immigration. Excerpt with highlights provided - -
The state of Illinois is investigating an automatic license plate reader system used in a northwest suburb after a Texas sheriff accessed the system to look for a woman who recently had an abortion.
This and hundreds of other searches, according to Secretary of State Alexi Giannoulias, violated Illinois law.
Police in Mount Prospect, a village in suburban Cook County, set up a license plate reader system in such a way that allowed other law enforcement agencies to access data without providing written attestations. In addition to the Texas case, Giannoulias office said Mount Prospects system had been searched 262 times for immigration-related reasons between mid-January and the end of April.
The Texas case came to light after a report from the tech outlet 404 Media found the search impacted more than 83,000 license plate reader cameras in multiple states.
Giannoulias also noted that 46 out-of-state law enforcement agencies conducted searches of Illinois records that violated state law.