Blog · Situations · 2026-07-31 · 2 min read

Corner lots, flag lots and unusable land

Square footage is not usable area. Where the difference is large, the assessment should reflect it.

Land assessment usually works from a rate per square foot within a neighbourhood. That works well for rectangles and badly for everything else.

Where the model struggles

Corner lots. Traditionally treated as more valuable — two frontages, better access. In residential use the reality is often the opposite: more pavement to maintain, more traffic on two sides, less privacy, and setback requirements on both frontages that reduce the buildable area.

Flag lots. A narrow access strip leading to a wider parcel behind. The strip is counted in the area and is worth very little.

Deep or narrow parcels. A 25-foot-wide lot may not be buildable at all under current zoning, however many square feet it contains.

Parcels with unusable portions. A ravine, a steep slope, a drainage channel, a wetland, a detention area, an easement crossing the buildable envelope.

The argument

Not that the rate per square foot is wrong, but that the area being priced is not all worth the same. Land you cannot build on, or cannot use, is worth a fraction of land you can.

So: establish the total area, establish how much is genuinely usable, and argue the unusable portion should carry a reduced rate or be excluded.

The evidence

A plat of survey. The foundational document — dimensions, easements, encroachments.
A wetland delineation or a FEMA flood map.
The zoning ordinance, showing setbacks and minimum lot dimensions.
The recorded easement itself.
A topographic survey where slope is the issue.
Photographs of the unusable ground.

Setbacks are the argument people miss

On a corner lot, front setbacks apply to both frontages. On a narrow lot, side setbacks can consume most of the width. The buildable envelope can be a small fraction of the parcel, and it is calculable from the ordinance and the survey.

A 50 × 150 lot is 7,500 sq ft. With 25-foot front and rear setbacks and 5-foot sides, the buildable envelope is 40 × 100 — 4,000 sq ft. On a corner with a second 25-foot front setback it drops to 20 × 100, or 2,000 sq ft. Same recorded area, a quarter of the usable land.

Uniformity still applies

Compare your land assessment per square foot against neighbouring parcels. If a regular rectangular lot of the same recorded area carries the same land value as your flag lot, that is the disparity — and it is easier to show than any argument about what the land is worth in absolute terms.

What to do

Get the plat of survey.
Calculate the buildable envelope under current zoning.
Identify and document every unusable portion.
Compare your land value per square foot against regular parcels nearby.
Present it as area that should not be priced as though it were buildable.

This is general information about how Illinois assessments and appeals work. It is not legal advice, not an appraisal, and not a prediction about your case. Deadlines and rules differ by county — check yours with your Board of Review.