GIS

When people search for “Cook County IL GIS,” they are usually trying to answer very practical questions: What is my property’s exact boundary? How has my parcel changed over time? What tax districts am I in? This guide walks through how Cook County’s geographic information system (GIS) tools work together—especially the main online map, CookViewer—so you can look up parcels, explore maps and data, and use the county’s official resources effectively, whether you are a homeowner, buyer, real estate professional, attorney, or planner.

Understand Cook County GIS and how it supports residents

Cook County’s Geographic Information Systems program is a countywide effort that ties maps, property records, and many other datasets together so they can be viewed and analyzed in one place.

The county’s Geographic Information Systems division describes its mission as optimizing the county’s investment in geospatial technology through collaboration, policy, planning, and services. In practice, that means:

Maintaining countywide parcel, road, and imagery datasets.

Making authoritative maps and GIS data available to county agencies.

Providing no-cost public access to property and land records through web applications.

Coordinating how GIS data is created, updated, and shared across departments.

Supporting applications used by the Assessor, Clerk, Board of Review, and other offices that depend on accurate maps.

Cook County’s enterprise GIS has been built out over decades. It began with automated road data in the late 1980s and expanded through the 1990s and early 2000s to a full parcel, planimetric (feature) and imagery repository. Today, the county uses a photogrammetric base (mapping from aerial imagery) and integrated workflows with the Assessor and Clerk to keep property information synchronized.

For you as a user, the most visible result of all this behind-the-scenes work is an interactive parcel map and a rich open data environment.

Start with CookViewer: the main interactive parcel map

The core online mapping tool for Cook County property information is the CookViewer property map. This application lets you zoom around the county, search for parcels, and see detailed information pulled from multiple offices.

CookViewer has a modern layout with flexible panels you can open, close, and resize so you can give more space to the map or to the data, depending on what you’re doing. When you first open the application, you can take a short guided tour that shows you the basic tools and layout.

Search by address, PIN, or intersection

At the top of CookViewer is a search bar. You can search in several ways:

Property Index Number (PIN):
10-digit PIN (for example, 1709461015)
14-digit PIN with or without dashes (for example, 17094610150000 or 17-09-461-015-0000)

Property address:
A standard street address, such as “69 W Washington, Chicago”

Street intersection:
Two street names, such as “W Washington St & N Dearborn”

Once you type your search:

Matching parcels appear in a Search Results panel.

Each result shows basic information like the 14-digit PIN and address.

When you click a result, the map automatically zooms to that parcel and opens the details panel.

If your search pulls up several properties—common with intersections or large buildings—just choose the exact parcel you need from the list.

Pick parcels directly on the map

You don’t always have to start from the search box. If you already know roughly where your property is, you can:

Click a parcel on the map to select it.

If you click once on a single parcel, its details open automatically.

If you click in an area with multiple stacked parcels (like condominiums), you’ll see a list of all those parcels so you can pick the right one.

For more control, use the Select Tool from the toolbar on the left:

Click once to select one or more parcels.

Click again on a selected parcel to remove it from your selection.

Drag a rectangle or draw a polygon to select many parcels across a block or neighborhood—helpful when you’re comparing properties or reviewing a larger area.

Explore detailed property information in the Property Details panel

Once you select a parcel, CookViewer opens the Property Details panel. This is where the “GIS” part really shines—information from several county systems is combined in one place.

Key sections typically include:

Location and zoning context

Here you can see:

Township and municipality
Zoning and related geographic context

This helps you understand which local government bodies and zoning rules apply to the property.

Tax details and assessed value

The panel includes rich assessment-related information, such as:

Property classification and land square footage

Assessor neighborhood

Current assessed values:
Land value
Building value
Total assessed value

There are also links out to related systems, such as Cook County’s open data for historical assessments, so you can see how a property’s value has changed over time.

If you need to dig deeper into assessment records, you can use the Cook County Assessor property search alongside CookViewer to cross-check PINs, appeal information, exemptions, and other assessment details.

Building characteristics and imagery

For many parcels, CookViewer shows:

Estimated building square footage
Construction type
Approximate age of buildings

Imagery tools are integrated so you can:

Jump to an oblique (angled) imagery viewer.

View a historical ground-level photo, when available, to see how the property looked in the past.

This combination of attributes and imagery is especially useful for verifying improvements, additions, or other changes.

Districts and political boundaries

CookViewer also brings in district information, including:

County Commissioner districts
Board of Review districts
School, library, park, and other tax districts

Through district information tools, you can see which entities you pay taxes to and which elected officials represent that property. That’s valuable for understanding your tax bill, local services, and who to contact with questions.

Use Cook County GIS tools to answer everyday property questions

Most users aren’t looking for abstract GIS concepts—they want specific answers. Here are some common tasks and how CookViewer helps.

Verify where your property begins and ends

If you’re planning a fence, garage, or addition, the parcel boundaries in CookViewer help you understand the official lot lines:

Search your PIN or address.

Zoom in on your parcel boundary.

Turn on relevant layers, such as parcel lines and aerial imagery, to see how the mapped boundary lines up with visible features like fences, driveways, or building corners.

For exact legal boundaries, you still rely on your deed, survey, or a licensed surveyor, but GIS gives a clear, visual starting point.

Check whether your assessment seems in line with similar properties

CookViewer includes a Property Comparison tool that lets you find similar properties based on:

Property class
Neighborhood
Square footage
Age or other characteristics

A typical workflow:

Open your property in the details panel.
Start the Compare Properties tool from the panel or left toolbar.
Confirm the pre-filled fields (PIN, township, neighborhood, class).
Adjust optional settings such as property size range or search radius.
Run the comparison to see a list of comparable parcels.

If no results appear, you can broaden the search by increasing the radius or loosening your filters. These comparisons can help you decide whether to learn more about an assessment or consider filing an appeal.

Understand which districts and services apply to your home

Because CookViewer is a GIS application, it doesn’t just show parcels; it also layers on district boundaries. You can:

See which school, park, library, and other taxing districts your property falls into.

View Commissioner and Board of Review districts.

Combine these with parcel and address information to understand how your taxes are distributed and which bodies manage services that affect you.

Turn on layers, history, and imagery for deeper insight

A major advantage of GIS over a simple online map is the ability to toggle different layers and time periods. CookViewer’s Layers and Imagery tools are key for this.

Control what you see with the Layers tool

The Layers tool lets you turn datasets on or off so the map focuses on what you care about. Typical layer groups include:

Parcel Archive layers by year (2000 to the current year)
Contours and Forest Preserve Districts
Places of interest (including county facilities)
Political boundaries (commissioner districts, townships, and more)
Taxing districts (school, park, library)
Highway systems and roads
Unincorporated zoning

Tips for using layers effectively:

Turn on only the layers you need to avoid clutter.

Expand a group to choose specific layers rather than turning everything on.

If a layer seems to be missing, zoom in closer—some layers only appear at certain scales.

You can temporarily hide the current parcel layer to make aerial imagery or other layers easier to see.

Examine parcel history with the Parcel Archive

The Parcel Archive is extremely helpful when you’re trying to understand how a property changed over time. For example, if several lots were consolidated into one, or if a subdivision split a larger parcel into many.

To use the archive:

Open the Layers panel.
Scroll to the Parcel Archive section.
Turn on the years you want to compare (for example, 2005 and 2025).
Look for differences in boundary shapes and labels.

Each year uses different colors, so you can visually compare how parcels were configured in different years—useful for research, legal work, or long-term planning.

Review change over time with aerial imagery

The Imagery tool lets you see aerial photographs for multiple years, going back as far as the late 1990s in many areas. This is useful for:

Checking when a structure was built or removed.
Seeing how land use has changed (for example, from vacant land to a development).
Reviewing driveway or parking layouts over time.

You can combine imagery with measurement tools:

Estimate distances, such as setbacks from the street.

Approximate the square footage of visible surfaces like roofs, parking areas, or additions.

While these measurements are approximate and not a substitute for a survey, they provide a quick way to sanity-check what you see in assessment records and permits.

Export, print, and share Cook County GIS maps and data

GIS isn’t just for viewing; CookViewer includes tools to export data and create map outputs you can share.

Export search results for analysis

From the Search Results or Property Details panel, you can:

Use Export to download a list of parcels as:
A CSV file (for spreadsheets or databases)
An Excel file

This is especially helpful if you:

Are reviewing multiple properties in a neighborhood.
Want to sort results by square footage, value, or classification.
Need to keep a record of comparable parcels you analyzed.

Once downloaded, you can use any spreadsheet software to further filter or chart the information.

Print maps and property reports

CookViewer’s Print tools support both mapping and reporting needs:

Print a map of:
A selected parcel, or
Any current map view (even without a selected parcel)

Print a report summarizing data for:
One property, or
All search results, if you choose that option

Basic steps:

Click the Print button on the right side of the application.

Give your map or report a title.

Choose a layout (for example, 11" x 8.5").

Select a format such as PDF.

Optionally:
Show the print area on the map.
Include all search results for a multi-parcel report.

Click Export and then download your file from the Print tab.

These outputs can be attached to emails, shared with clients or colleagues, or brought to meetings and hearings.

Go beyond CookViewer with Cook Central maps and open data

Cook County’s GIS effort is more than a single web map. There is also a broader open data and application environment called Cook Central.

The Cook Central maps and data hub centralizes:

Downloadable datasets (for example, parcels, boundaries, transportation)
Thematic applications (maps focused on particular topics)
Imagery and place-of-interest data
Printable maps and other GIS resources

You can browse through categories like:

Property and land records
Boundaries and districts
Transportation
Natural environment and recreation
Imagery and places of interest

If you prefer to start from the main county website, the Cook Central county maps and data page also serves as a gateway to maps and geospatial data.

This environment is especially useful if you:

Need to integrate county GIS data into your own systems.

Are a developer or analyst building tools around county information.

Want to explore specialized applications, such as project story maps or topic-specific dashboards.

Connect Cook County GIS with other county services

The GIS system doesn’t exist in isolation. It supports and connects with many other services that affect property owners and residents.

Examples include:

Property tax and assessment information from the Assessor.

Land records and recordings from the Clerk’s office.

Countywide maps and datasets that support planning, environmental work, transportation, and emergency response.

To understand how GIS fits into the larger county government, you can explore the Cook County Government homepage and navigate through services such as property and housing, environmental work, roads and transportation, and more. Many of the applications and services in these categories rely on underlying GIS data for accurate mapping.

For formal data requests related to offices under the President (which includes the Bureau of Technology and GIS), the Freedom of Information Act request portal for offices under the President provides information about submitting FOIA requests.

How Cook County GIS is organized and maintained

The county’s GIS program is part of the Bureau of Technology and is closely linked to other offices that manage property and land information.

Key points about how it operates:

Enterprise coordination: GIS data is maintained in a shared enterprise environment, so departments work from the same base maps and datasets.

Quality control: The GIS division implements quality control measures to ensure parcel boundaries, imagery alignment, and attribute data meet standards.

Infrastructure investment: The county invests in servers, networking, and web map applications to support both internal staff and public users.

Support for municipalities: Municipalities within the county can obtain data for their own jurisdictions, promoting consistent mapping across local governments.

When you use CookViewer or download data from Cook Central, you’re tapping into this coordinated system.

Departments and offices connected to Cook County GIS

Cook County Assessor’s Office – 118 North Clark Street, Room 320, Chicago, Illinois 60602 – (312) 443-7550

Cook County Clerk’s Office (Maps and Tax Services) – 118 North Clark Street, Room 434, Chicago, Illinois 60602 – (312) 603-5640

Cook County Clerk’s Recordings Division – 118 North Clark Street, Room 120, Chicago, Illinois 60602 – (312) 603-5050

Cook County GIS FAQs

How do I quickly find my property or PIN on the county’s map?

Start with the county’s official CookViewer application, which is the primary online parcel map for property information. Use the search bar to enter either a 10-digit or 14-digit Property Index Number (PIN), a full street address, or a street intersection; matching properties will appear in a results panel you can click to zoom the map and open details. Access the map at the official CookViewer property map.

What information can I see once I open a parcel in CookViewer?

When you select a parcel, the Property Details panel displays location information (township, municipality, and zoning context), assessment-related data (property class, land square footage, and current assessed values), links to historical assessed values, and building characteristics such as estimated square footage, construction type, and age. You can also open oblique aerial imagery and historical photos, plus links to Clerk property records, the property tax portal, and other county data resources directly from this panel.

How can I use Cook County GIS tools to compare my assessment with similar properties?

From the Property Details panel, choose the Compare Properties tool. CookViewer will prefill key fields like PIN, township, neighborhood, and property class, and you can fine-tune the search by adjusting size, characteristics, or radius to find comparable parcels. If no results appear, broaden the search area or relax your filters. For deeper assessment research, you can pair this with the Assessor’s online tools linked from the map, such as the Assessor property search and forms.

Where can I see historic parcel boundaries and aerial imagery for research or disputes?

Use the Layers tool in CookViewer to turn on yearly Parcel Archive layers, which show how parcel boundaries and labels looked from 2000 through the current year. Different colors help you visually compare subdivisions, consolidations, or boundary adjustments over time. The Imagery tool lets you toggle aerial photos going back to the late 1990s and measure distances or approximate areas, which is useful when reviewing improvements, driveways, or development patterns.

Where can I download Cook County GIS data and explore other official applications?

Beyond the parcel viewer, the county’s open data hub Cook Central centralizes downloadable datasets, imagery, boundary layers, transportation data, printable maps, and a gallery of interactive applications built by the GIS division. You can browse property and land records, boundaries and districts, environmental data, and more at the official Cook Central maps, apps, and data hub. For an overview of the program’s mission and mandates, visit the county’s Geographic Information Systems page.