Who actually set your value: township assessor, Supervisor of Assessments, or Board of Review
Three offices, three different jobs. Sending your argument to the wrong one wastes the only window you get.
Illinois splits assessment across offices, and owners routinely address the wrong one.
The township assessor
Sets the original value for parcels in that township. This is who to talk to first and informally. If the record has your building size wrong, the assessor can often simply fix it — no hearing, no filing, no deadline pressure. A large share of successful outcomes never become appeals at all.
The county Supervisor of Assessments
Oversees the township assessors, applies county-wide changes, maintains the roll, and publishes assessments. In counties without township assessors, this office does the assessing. It is also the office to FOIA if you want the roll as an electronic file.
The Board of Review
An independent body that hears formal appeals. It can lower, sustain — or raise — an assessment. It is not the assessor and does not work for the assessor.
The order that works
Call the township assessor with a factual error. File with the Board of Review when you disagree about value or uniformity, or when the assessor will not correct the record. Going straight to the board with something the assessor would have fixed in a phone call is slower and riskier — because the board can review the whole assessment, not just the part you complained about.
Beyond the board sits the Property Tax Appeal Board, and beyond that the circuit court.