How to download assessment data from your county website

Last updated 2026-07-10

Why would you want to download county assessment data?

Your tax bill runs on a value the county set, often without anyone ever stepping inside your home. That value can be wrong. Winning an appeal means showing the assessor (or a review board) that comparable homes nearby are assessed lower, or that recent sales in your neighborhood put your home below what the county claims.

To prove that, you need numbers. more than your own parcel, and your neighbors' assessed values, square footages, lot sizes, and sale prices. That raw evidence is what wins appeals.

Here's the part nobody tells you. Every county in the United States has to keep property assessment records as public records under state open-records law. ^[1] Most have posted at least some of it online. You can pull it yourself, for free, in an afternoon. No consultant. No contingency fee eating 30 to 40 percent of your refund.

Once the data is in front of you, filter for homes like yours, calculate their assessed values per square foot, and build a comps table that goes straight at your own number. This is the same raw material paid consultants use. The only thing they have that you don't is reps.

What types of assessment data do counties actually post online?

County assessors publish several overlapping kinds of data. Knowing which one you need saves an afternoon.

Parcel-level assessment rolls. The master list: every taxable parcel in the county, with assessed value, owner name, property address, land use code, building size, and year built. Many large counties release this as an annual bulk file, sometimes called the 'assessment roll,' 'grand list,' or 'appraisal roll.' ^[2]

Sales data. Recorded deed transfers with sale price and sale date. Some counties bundle this with the assessment roll; others publish it separately through the county recorder or register of deeds. This is your strongest evidence for comparables.

GIS parcel layers. Shapefiles or web-map exports that tie spatial data to assessment attributes. Handy if you want to map comparables within a set radius of your home.

Sketches and field cards. Scanned record cards showing the assessor's notes about your property: bedroom count, bathroom count, condition grade, and the measurements used to estimate value. Errors here are common, and correctable.

Tax rolls and billing data. The actual tax billed to each parcel, broken out by taxing district. Good for confirming your exemptions applied.

Not every county publishes all five. Rural counties sometimes only have a parcel search tool with no bulk download. When that happens, a public records request is your fallback, covered below.

How do you find the download page on your county assessor's website?

Start at the county assessor's main site. A search for '[your county name] county assessor' or '[county name] county appraisal district' almost always puts it in the top result. ^[3]

Once you're there, hunt for any of these menu items or page titles:

• Data Downloads
• Open Data
• Assessment Roll Download
• Public Records
• GIS Data
• Property Data Export
• Appraisal Roll (common in Texas)

No luck? Try the county's general open data portal. Many counties moved bulk data to a central portal separate from the assessor's page. Search '[county name] open data portal' or '[county name] data catalog.' Cook County in Illinois, for example, hosts its assessment data on a dedicated platform at data.cookcountyil.gov. ^[4]

If the assessor site has a search box, type 'download' or 'export.' Some counties bury the link in a FAQ or a 'Resources' tab.

One honest caveat. Smaller counties, roughly those under 50,000 parcels, often have no bulk download at all. Their data lives only in a parcel-by-parcel search screen. In that case you have two moves: a public records request (most states require a response within 5 to 10 business days) or a manual lookup of the 10 to 20 closest comparables one at a time. Tedious, but it works fine for a single appeal.

What does the county-by-county download process look like in practice?

The process varies more than it should. Here's a realistic picture for several large counties, based on how their portals are currently set up.

County	Data portal location	Download format	Notes
Cook County, IL	data.cookcountyil.gov	CSV, GeoJSON	Annual assessment roll; sales data separate [4]
Los Angeles County, CA	assessor.lacounty.gov	TXT (fixed-width), CSV	'Assessor Parcels Data' link under Open Data [5]
Harris County, TX (Houston)	hcad.org	CSV, Excel	Full appraisal roll download on main page [6]
Maricopa County, AZ	mcassessor.maricopa.gov	CSV	'Data Download' tab; parcel & sales files
New York City	nyc.gov/finance	CSV, Excel	PLUTO dataset via NYC Open Data; all 5 boroughs [7]
King County, WA (Seattle)	info.kingcounty.gov	CSV, Access DB	Parcel, sales, and building files; data dictionary included
Dallas County, TX	dallascad.org	CSV	Appraisal export in 'Reports & Data'
Hennepin County, MN	hennepin.us	Various	Property tax data via county GIS portal [8]

For LA County, the LA County assessor data comes as a large TXT file. You'll need the data dictionary (posted on the same page) to know what each column means, because the field names are coded.

For Cook County, the assessor's open data site keeps separate tables for residential assessments, commercial assessments, and sales. You join them on the parcel identifier (PIN in Cook County). The Cook County tax assessor portal also lets you look up individual parcels if you only need a handful of comps rather than the whole roll.

Texas appraisal districts are unusually good about bulk data. Texas Tax Code Section 25.19 requires the district to make its appraisal roll available to the public. ^[9] Harris County Appraisal District posts an annual export that typically runs past 400,000 parcels. ^[6]

How do you actually download and open the files?

Bulk assessment files run big. The LA County parcel file is over 2 GB uncompressed. A few practical tips.

Use the right tool. Excel opens CSV files up to about 1 million rows, which covers most county files. If your county file runs bigger than that (rare, but it happens in the largest counties), or if it's an Access database (.mdb/.accdb), you'll need Microsoft Access, LibreOffice Base, or a free tool like DB Browser for SQLite. For plain filtering without formulas, Google Sheets handles files up to about 10 million cells.

Download, don't stream. Right-click the link and save it to your computer. Don't try to open a multi-gigabyte file straight in your browser.

Find the data dictionary. This is the document that decodes each column. 'EFFYR' might mean effective year built. 'IMPVAL' might mean improvement value. Without the dictionary, the file is gibberish. Most counties post it as a PDF on the same page as the download. If you can't spot it, search the page for 'layout,' 'schema,' 'codebook,' or 'field descriptions.'

Filter first. Once the file opens, filter by land use code (residential single-family is often 0100 or similar) and by neighborhood or zip. You don't need 400,000 rows. You need the 200 to 500 parcels near you that share your home's characteristics.

Sort by assessed value per square foot. Add a calculated column: assessed value divided by living-area square feet. Sort by it. Homes similar in size, age, and location that land below yours are your comparables.

What if your county has no bulk download and you need a records request?

No export and no open-data portal? You're not stuck. Every state has a public records law that covers assessment data.

In most states you send a written request to the county assessor's office asking for the parcel data in electronic format. The exact law varies. California's Public Records Act (Government Code Section 6250 et seq.) requires agencies to respond within 10 days. ^[10] Texas Government Code Chapter 552, the Public Information Act, requires a response within 10 business days. ^[11] Most other states land in a similar range.

The request doesn't have to be fancy. A short email works. Give your name, the data you want (parcel assessment roll in electronic format, CSV or Excel preferred), and a line saying you're requesting it under your state's public records law. Agencies can charge for the actual cost of reproduction, but they can't charge you for public data simply being public.

Some counties push back and claim the data is proprietary, or that only certain fields are public. That's generally wrong for assessment records, which most state statutes make explicitly public. If you hit resistance, cite your state's specific open-records statute in a follow-up email.

For Bexar County and Gwinnett County readers, both counties run fairly accessible online portals. But if you're in a smaller jurisdiction nearby, the public records route is often your fastest path.

How do you find comparable sales data specifically?

Assessment records tell you what the assessor thinks each property is worth. Sales records tell you what buyers actually paid. You want both, ideally in the same spreadsheet.

Sales data usually sits in one of three places:

1. Bundled into the county's assessment download (many Texas appraisal districts do this) 2. Posted separately by the county recorder, register of deeds, or clerk 3. Published by your state's department of revenue or tax equalization board as a statewide sales file

New York State posts annual Residential Assessment Ratios and sales files by municipality through the Office of Real Property Tax Services. ^[12] Minnesota's Department of Revenue posts a statewide sales ratio study each year. ^[13] These state-level files can fill gaps in what your county puts out.

Once you have sales data, filter it down. Aim for the 12 to 24 months before your assessment date (that date varies by state, but January 1 of the assessment year is common), properties within roughly one mile of your home, and homes within about 20 percent of your square footage and lot size. Five to ten solid comparable sales is enough to build a case.

For Santa Clara County and Hennepin County residents, both counties post sales data through their GIS portals alongside parcel data.

How do you spot assessment errors in the raw data?

This is where the download earns its keep. Once you have the assessor's record for your property, compare it line by line against reality.

Common errors in field cards and parcel data:

Wrong square footage. The file says 2,400 square feet; your home is 1,950. This happens more than you'd guess, especially in older neighborhoods where additions and teardowns weren't logged consistently. Inflated square footage means an inflated value, proportionally.

Wrong bedroom or bathroom count. A three-bedroom recorded as a four-bedroom climbs the value scale it shouldn't.

Wrong land size. Lot square footage or acreage pulled from old plats can be off, especially on irregular lots.

Wrong year built. Age drives depreciation in most assessor models. A 1955 home recorded as 1975 gets less depreciation than it's owed.

Wrong condition or quality grade. Assessors assign grades (Fair, Average, Good, Very Good, Excellent) that multiply the base value. A home graded 'Good' that's really 'Average' can swing the value 10 to 20 percent.

To check your own field card, look for a 'Property Detail' or 'Parcel Card' link on your county's parcel search. Some counties post a scanned image of the physical card. Download it, print it, and walk every field.

TaxFightBack's DIY appeal kit includes a field-card review checklist that runs you through this comparison in order, if you want a structured approach.

For Montgomery County homeowners, the county's online portal shows field-card data right in the parcel detail screen, so you don't have to download the bulk file just to check your own record.

How do you organize downloaded data to build a comps table for your appeal?

A review board wants a clean, readable comparison. Raw spreadsheet dumps don't land. Here's a simple workflow.

Step 1. In your downloaded file, filter to your neighborhood and property type. Note your parcel's key attributes: living area, lot size, year built, style (one-story vs two-story), and condition grade if it's visible.

Step 2. Find 5 to 10 comparable parcels. The best ones sold in the past two years at prices below your assessed value, that's the most direct evidence. If no sales are available, neighboring homes assessed lower per square foot also work.

Step 3. Build the comparison table. Columns: Address, Sale Date, Sale Price, Assessed Value, Living SF, Assessed Value per SF, Sale Price per SF. Your property goes in the top row.

Step 4. If your assessed value per SF sits above your comparables' assessed values per SF, you have a prima facie case. The gap is your argument.

Step 5. Print the table and attach the assessor's own data as the source. You're turning the county's numbers against the county. That's hard to argue with.

The International Association of Assessing Officers (IAAO) sets the mass-appraisal standard for residential property at a coefficient of dispersion (COD) below 15, meaning individual assessments shouldn't vary more than about 15 percent from the median level of appraisal in the area. ^[14] If your comps table shows you assessed 20 percent or more above similar properties, you're outside that standard and you have a strong basis for a reduction.

Are there free third-party tools that aggregate county assessment data?

Yes, several. Each has limits.

Regrid (regrid.com) aggregates parcel data for the entire United States. The free tier lets you look up individual parcels. Paid plans let you export in bulk. Good for counties that offer no download of their own.

ProPublica's assessments reporting and state-specific investigative tools sometimes post cleaned assessment data for major metros, usually after coverage of assessment inequality.

Zillow and Redfin show assessed values on property pages (pulled from public records) plus recent sales. Not bulk-downloadable for free, but useful for a quick sanity check.

ATTOM Data Solutions and CoreLogic sell bulk property data commercially. Prices run into hundreds of dollars per month for full county exports. Skip it for a single appeal.

State open data portals. California, New York, Minnesota, and others run central data repositories (data.ca.gov, data.ny.gov) that sometimes include assessment or sales data pulled from county sources.

The honest ranking: for a single-property appeal, go to your county assessor's site first. Third-party aggregators earn their spot when your county has no bulk download and you need comparable data quickly. For watching your assessed value year over year, Regrid's free tier is genuinely useful.

For NYC property tax and Los Angeles County property tax research, the city and county open-data portals are rich enough that third-party tools add little beyond convenience.

What are the privacy limits on publicly posted assessment data?

Property assessment data is public record. Owner name, mailing address, assessed value, and property characteristics are all legally accessible to anyone. Some states redact owner information in bulk downloads (Florida restricted some data access after a 2023 legislative change), but assessed values and property attributes stay public.

A few narrow exceptions exist. Certain protected individuals (judges, law enforcement officers, domestic violence survivors) can apply to shield their home address from public property records in states like California (AB 1033 and similar statutes) and Texas (Tax Code Section 25.025). ^[15] A redacted or scrambled address in a county file is usually why.

For everyone else, nothing stops you from downloading, analyzing, and presenting this data in an appeal. Using public government data is your right.

What should you do after you have the data?

Downloading the data is step one. What you do next decides whether you get a reduction.

First, file your appeal before the deadline. Appeal deadlines are strict and vary by state. In most states they run 30 to 90 days from the date your assessment notice was mailed. Miss it and you wait a full year. Confirm your exact deadline with your county assessor's office or your state department of revenue.

Second, build your evidence packet: your field-card review showing any errors, your comps table, and supporting documents (a recent appraisal, photos of condition problems, a contractor estimate for deferred maintenance).

Third, submit. Most counties now take appeals online. Some still require a paper form. The form asks for your parcel number, your opinion of value, and your supporting evidence.

The TaxFightBack DIY appeal kit runs the whole evidence-to-submission process with templates, so you're not building the packet from a blank page. The comparable-sales table template matches the format most county review boards expect.

For ongoing reference, the St. Louis County personal property tax page and the Bibb County tax assessor page both cover county-specific appeal procedures in detail if those are your jurisdictions.

Frequently asked questions

Is county property assessment data really free to download?

Yes. Assessment records are public records under state law in all 50 states. The data itself is free. Some counties charge a nominal reproduction fee for physical copies, but electronic downloads from county websites cost nothing. You don't need to pay a consultant or data vendor to reach your county's own assessment roll.

What file format does county assessment data usually come in?

Most counties post data as CSV (comma-separated values) or fixed-width TXT files. Some use Excel (.xlsx). A few larger counties offer GIS shapefiles or Access databases. CSV is the most common and opens directly in Excel, Google Sheets, or any spreadsheet program. Always look for a data dictionary or layout guide on the same download page.

My county website has no download link. How do I get the assessment data?

Send a written public records request to your county assessor's office, citing your state's open-records law. Email works. Ask for the parcel assessment roll in electronic format (CSV or Excel). Most states require a response within 5 to 10 business days. You can request data for the whole county or limit it to specific neighborhoods or parcel ranges.

How do I find my own property's assessed value and field card?

Go to your county assessor's website and use the parcel search tool, usually searchable by address or parcel number. The detail screen shows assessed value, property characteristics, and often a scanned field card. You don't need to download the bulk file just to check your own record. The bulk download matters when you need comparable properties.

How many comparable properties do I need for a property tax appeal?

Five to ten is generally enough. More isn't better if the extra properties are less similar to yours. Focus on recent sales (within 12 to 24 months of your assessment date) of homes close in size, age, location, and condition. A tight set of 5 good comparables beats 20 weak ones every time.

Can I use Zillow or Redfin data instead of downloading county data?

For quick reference, yes. Zillow and Redfin pull assessed values and recent sales from public records and show them on property pages. But they aren't bulk-exportable for free, and their data can lag the county's actual records. For a formal appeal, using the county's own data file as your source is cleaner and harder to dispute.

What is a parcel number and why do I need it?

A parcel number (also called APN, PIN, folio number, or tax ID) is the unique identifier the county assigns to each property. You need it to look up your own record in the bulk file, to search the assessor's portal, and to identify the correct parcel when you file an appeal. Find yours on your property tax bill or your deed.

How current is the data on county assessment portals?

Most counties update their online parcel data annually, after the assessment roll is certified for the tax year. Sales data often updates more often, sometimes quarterly. If you're preparing an appeal for the current tax year, confirm the file's 'as-of' date, usually noted on the download page or inside the file, before you rely on the values.

What is a coefficient of dispersion and why does it matter for my appeal?

The coefficient of dispersion (COD) measures how consistently properties in an area are assessed relative to market value. The IAAO sets the standard COD below 15 for residential property. If your comps table shows you assessed well above the median level for similar nearby homes, you're arguing the assessment breaks that uniformity standard.

Can I use county data to challenge my assessment in small claims court if the informal appeal fails?

Yes. In states that allow property tax appeals in small claims or tax court (Texas, California, and many others), the same downloaded county data, labeled with its source, is admissible evidence. Print your comps table, attach the assessor's own data export as Exhibit A, and present it directly. You don't need an appraiser for an informal hearing, though one helps in formal court.

Does downloading assessment data work for commercial property appeals too?

Yes, though the analysis is harder. Commercial properties are often valued by the income approach rather than comparable sales, so you'll want income and expense data on top of assessed values. Many counties post commercial assessment data in the same bulk file as residential. Look for land-use codes for retail, office, or multifamily. The download is identical; the analysis layer is where it gets tricky.

How do I figure out which neighborhood or zone my property belongs to for filtering the data?

Your parcel record usually includes a neighborhood code, tax district code, or census tract number. Note those values from your own record, then filter the bulk file to the same code. Or filter by zip code, or by a geographic radius if the file includes latitude and longitude (many GIS-enabled exports do).

What does 'assessment ratio' mean in county data, and should I care?

Assessment ratio is the percentage of market value at which properties are supposed to be assessed. Many states assess at 100 percent of market value; others use a fixed fraction (Louisiana uses 10 percent for residential, for example). If your county assesses below 100 percent, compare your assessed value to the ratio-adjusted values of your comparables, not the raw numbers. The ratio should be posted on the assessor's website.

Sources

1. NCSL, Open Records Laws by State Overview: Every state has a public records law requiring government records, including property assessment rolls, to be available to the public.
2. International Association of Assessing Officers (IAAO), Glossary for Property Appraisal and Assessment: Assessment rolls (also called appraisal rolls or grand lists) are the official county record of all taxable parcels and their assessed values.
3. IAAO, Standard on Assessment Administration: County assessors are the primary government entity responsible for maintaining and publishing property assessment records.
4. Los Angeles County Assessor, Assessor Parcels Data download page: Los Angeles County Assessor posts its parcel file in TXT and CSV format under the Open Data section of its website.
5. Harris County Appraisal District (HCAD), Property Data Downloads: Harris County Appraisal District provides a full annual appraisal roll export in CSV and Excel formats on its main website.
6. Hennepin County, Minnesota, Property Tax and Assessment Data: Hennepin County posts property tax and assessment data through its GIS portal for public download.
7. Texas Tax Code Section 25.19, Notice of Appraised Value: Texas Tax Code Section 25.19 requires appraisal districts to make the appraisal roll available to the public, and the statute states that appraisal records 'are available to the public.'
8. California Government Code Section 6250, California Public Records Act: California's Public Records Act requires government agencies to respond to public records requests within 10 calendar days.
9. Texas Government Code Chapter 552, Public Information Act: Texas Government Code Chapter 552 requires governmental bodies to respond to public information requests within 10 business days.
10. New York State Office of Real Property Tax Services, Residential Assessment Ratios and Sales Files: New York State ORPTS posts annual residential assessment ratio studies and sales files by municipality for public download.
11. Minnesota Department of Revenue, Sales Ratio Study: Minnesota's Department of Revenue publishes an annual statewide sales ratio study showing median assessment ratios and coefficients of dispersion by county.
12. IAAO, Standard on Ratio Studies (2013), Section 4.3: The IAAO standard for residential property assessment sets an acceptable coefficient of dispersion (COD) of below 15.0, meaning individual assessments should not vary more than 15 percent from the median level of appraisal in the area. The standard states: 'For single-family residential properties in larger, more homogeneous jurisdictions, the COD should be 15.0 or less.'
13. Texas Tax Code Section 25.025, Confidentiality of Certain Home Address Information: Texas Tax Code Section 25.025 allows certain protected individuals, including peace officers and judges, to request that their home address be kept confidential in appraisal records.