JB PARCELHow property assessment data works, in any state
Every county in the country taxes property, so every county keeps a record of who owns each parcel, where to mail the bill, what the property is worth, and what is on it. That record, kept by an assessor, appraiser, or auditor depending on the state, is the most complete dataset about real estate that exists. It is also built for one purpose, fair taxation, which explains both its strengths and its blind spots.
The fields every county keeps
| Field | What it is | How reliable |
|---|---|---|
| Owner name | The name on the last recorded deed the assessor has processed | High, but weeks to months behind the deed record |
| Mailing address | Where the tax bill goes | Very high: the county has a financial reason to keep it right |
| Parcel id | The county's key for the lot; formats differ by county | Stable unless parcels split or merge |
| Land and improvement value | The assessor's market estimate, split between dirt and buildings | Good relative to neighbors; lags the market between reappraisals |
| Assessed value | The taxable number after the state or county's ratio | Exact; the tax is computed on it |
| Last sale date and price | The most recent transfer the assessor recorded | Usually only the last one, and non-market transfers are mixed in |
| Acreage, land use, class | Size and the assessor's category | Acreage is from the deed; class is a tax category, not zoning |
| Year built, square footage, building details | The appraiser's measurements and codes | Good where published; several large counties do not publish them for free |
Why the same field looks different across the line
Assessment is local. Some states run a statewide system and publish one file (Tennessee's Comptroller covers 86 of 95 counties; North Carolina and Arkansas publish statewide parcel layers). Others leave every county on its own software, so the field names, codes, and even whether the data is free change at the county line. A few large counties anywhere will lock building details behind a records request. The honest answer to "how complete is your data" is always "per county," which is why our parcel cards say, field by field, when a county does not publish something.
What assessment data is good at
- Who owns what, and where they get mail. The foundation of every off-market strategy.
- Relative value. The assessor is trying to be consistent across a county, so a parcel assessed well below its neighbors usually is worth less, for a reason you can go find.
- Land versus building. When land is most of the value, the building is in the way. That is the teardown and redevelopment screen.
- Tenure. A last sale twenty years ago tells you about the owner's situation.
- Scale. You can ask a question of every parcel in a county at once, which no listing site lets you do.
What it is bad at
- Timing. A sale last month is probably not there yet. A renovation done without a permit is never there.
- Market value today. Use the appraisal for ranking, not for pricing.
- History. Most counties publish only the last sale. Prior owners and prices live at the recorder of deeds.
- Anything about the person. Phone numbers, emails, and circumstances are not in the file, and the law treats them differently from the public record.
Reading a card without fooling yourself
Start with land share of value and years since the last sale. Then check the mailing address against the property address. Then the building fields, remembering they describe the original construction. Then zoning and flood, which come from other offices entirely. If a field is blank, find out whether the county publishes it before you read the blank as "none." Our cards do that last step for you.
50 states, 151.0 million parcels, with each field labeled honestly when a county leaves it out.
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