Farmland is not assessed on what it would sell for
Illinois assesses farmland on agricultural economic value from soil productivity, not sale price.
Farmland follows an entirely separate statutory scheme, and applying residential logic to it produces nonsense.
The basis
Farmland is assessed on agricultural economic value — derived from soil productivity indexes and expected income from farming — rather than on market value. A sale price nearby is largely irrelevant.
Soil productivity
Each soil type carries a productivity index, and the assessment follows it. Two visually similar fields can be assessed quite differently because their soils differ, and that is the system working as designed.
Use categories
Cropland, permanent pasture, other farmland and wasteland are treated differently. Land mapped in the wrong category is a genuine and checkable error.
Where appeals succeed
Usually on facts: acreage in the wrong category, land mapped as tillable that is not, a soil classification that does not match the actual soil, or acreage that is simply wrong. Arguing that the farm would not sell for the implied value is not an argument here.
The boundary case
A farmhouse and its home site are assessed residentially while the surrounding acreage is assessed as farm. Where that line is drawn matters, and it is worth checking that the residential portion is not larger than it should be.