Using Illinois FOIA to get the assessment roll
Assessment records are public. Ask for the electronic file, and cite the subsection that requires it.
Where a county publishes little online, the records still exist and the Freedom of Information Act reaches them.
Who to ask
The county Supervisor of Assessments — not the County Clerk, who holds rates, and not the Treasurer, who holds bills. The roll belongs to the Supervisor of Assessments.
Ask for the electronic file
Illinois FOIA requires a public body to provide records in the electronic format they are kept in, when asked. Cite that. It is the difference between a CSV by email and a fee for a printout of forty thousand rows.
Name the fields
"The assessment roll" invites a summary. Ask specifically: PIN, site address, city, ZIP, class code, assessed land, assessed improvement, assessed total, assessment year, and — where the office maintains it — building square footage and year built.
Fees and timing
A response is due within five business days, extendable by five more. Ask to be contacted before any fee is incurred.
What it is good for
Uniformity analysis. With the roll you can compute assessed value per square foot across an entire township and see precisely where you sit — which is the same thing the assessor can see and you otherwise cannot.