Johnson County, Illinois GIS Map
This GIS map of Johnson County, Illinois (IL) shows the official Census county boundary (FIPS 17087), with federal layers you can switch on for FEMA flood zones, USGS elevation contours and hillshade, NLCD land cover, and school district lines.
Johnson County has a population of about 13,376 (U.S. Census Bureau, 2020-2024 ACS 5-year estimate) and a land area of 343.7 square miles. Use the inspect tool to read coordinates, elevation and the layers under any point.
- State
- Illinois (IL)
- Population
- 13,376
- Land area
- 343.7 sq mi
- Density
- 39 / sq mi
- Coordinates
- 37.4607, -88.8821
- FIPS code
- 17087
Johnson County is not the only one — there are 11 other states with a county of the same name. Compare every Johnson County.
Johnson County Demographics
Source: U.S. Census Bureau, American Community Survey 2020-2024 5-year estimates.
Population
13,376
Households
4,101
Median household income
$62,528
Median age
41.4 years
Median home value
$160,500
Median gross rent
$781/mo
Owner-occupied homes
82%
Bachelor's degree or higher
19.6%
Below poverty level
17.6%
Land area
343.7 sq mi
Population density
39 / sq mi
Johnson County Population Growth
Source: U.S. Census Bureau, 2010 Census and Population Estimates Program (Vintage 2024: April 2020 estimates base and July 1, 2024 estimate).
2010 Census
12,582
April 2020 (estimates base)
13,307
July 2024 estimate
13,320
Change 2010-2020
+5.8%
Change 2020-2024
+0.1%
Natural Hazard Risk in Johnson County
FEMA National Risk Index ratings for Johnson County, compared with all U.S. counties.
Overall risk
Score 51.1 of 100
Expected annual loss
Buildings, population & agriculture
Social vulnerability
Susceptibility to hazard impacts
Community resilience
Ability to prepare & recover
Risk by Hazard
- EarthquakeRelatively Moderate
- Heat WaveRelatively Low
- Strong WindRelatively Moderate
- Ice StormRelatively Moderate
- HailRelatively Low
- Winter WeatherRelatively Moderate
- Cold WaveRelatively Low
- TornadoRelatively Low
- DroughtRelatively Low
- LandslideVery Low
- HurricaneVery Low
- Inland FloodingRelatively Low
- LightningRelatively Low
- WildfireVery Low
Source: FEMA National Risk Index (December 2025 release). County-level ratings are relative to other U.S. counties and are not a property-specific assessment.
Environmental Conditions in Johnson County, Illinois
Radon potential, monitored air quality and current drought status for Johnson County, Illinois, from the Environmental Protection Agency and the U.S. Drought Monitor.
Radon potential
Zone 2
moderate radon potential
EPA predicts an average indoor level between 2 and 4 pCi/L, so the EPA recommends testing, because elevated levels are still found in some homes here.
Drought status
Moderate drought in 85.1% of the county
Drought Severity and Coverage Index 185.1 of 500.
- D0 Abnormally dry14.900000000000006%
- D1 Moderate drought85.1%
Map of 13 October 2026.
Sources: EPA Map of Radon Zones (September 2025), EPA Air Quality Index (2024) and the U.S. Drought Monitor. A radon zone is a regional planning tool, not a prediction for any individual home — the EPA recommends testing every home regardless of zone. Air quality is shown only for counties that host an EPA monitor. Drought figures describe one weekly map, not a long-term climate average. Compare counties in Illinois.
GIS Data for Johnson County, IL
The Johnson County GIS map on this page loads live federal layers in your browser, so you can check flood zones, terrain, land cover and district boundaries anywhere in Johnson County without a separate GIS login. All of the Johnson GIS data below is drawn from public U.S. government sources.
Layers you can turn on
FEMA flood zones
National Flood Hazard Layer — flood insurance rate map zones and floodways.
Elevation contours and hillshade
USGS 3DEP terrain, so you can read slope and relief across the county.
Land cover
NLCD land cover classes — forest, developed, wetland and water.
School districts
Census TIGER unified and elementary school district boundaries.
ZIP code and county boundaries
Census TIGER ZCTA and county boundary lines.
Map tools
Measure distance and area
Draw a line or polygon to get length in miles or area in acres.
Sketch and annotate
Add points, lines and shapes on top of the map.
Inspect any point
Click the map to read coordinates, elevation and the layers under your cursor.
Download the map
Save the current view as a PNG image.
Where the data comes from
County boundaries come from the U.S. Census Bureau TIGER/Line program, flood zones from FEMA's National Flood Hazard Layer, terrain from the USGS 3D Elevation Program, land cover from the Multi-Resolution Land Characteristics Consortium, and demographics from the American Community Survey.
Property records and tax maps in Johnson County
Most people who look up Johnson County GIS data are after parcel-level records: who owns a property, what it last sold for, and what it is assessed at. Those records are kept locally, not federally, so they are not part of this map. Johnson County property and tax map data lives with the county's own records office, and what that office is called varies by state — Texas counties run an appraisal district (usually searched as a “CAD”), Kentucky uses a Property Valuation Administrator (PVA), and most other states use a county assessor, auditor or tax office. Start with that office for a deed, a tax map number or a parcel boundary; use the map above for flood zones, elevation and land cover on the same land.
Johnson County FAQ
What state is Johnson County in?
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Johnson County is a county in Illinois (IL).
What is the population of Johnson County?
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Johnson County, Illinois has a population of about 13,376, according to the U.S. Census Bureau American Community Survey.
How big is Johnson County?
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Johnson County covers about 343.7 square miles of land, with a population density of roughly 39 people per square mile.
What is the FIPS code for Johnson County?
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The FIPS county code for Johnson County, Illinois is 17087. It is used to identify the county in federal datasets such as Census TIGER and FEMA flood maps.
What is the median household income in Johnson County?
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The median household income in Johnson County, Illinois is about $62,528 per year.
What is the radon zone for Johnson County?
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Johnson County is in EPA radon Zone 2, meaning the EPA predicts an average indoor radon level between 2 and 4 pCi/L. In this zone the EPA recommends testing, because elevated levels are still found in some homes here. The EPA is clear that a radon zone is a regional planning tool and not a prediction for any individual home.
Is Johnson County in a drought?
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As of the 13 October 2026 U.S. Drought Monitor map, moderate drought covers 85.1% of Johnson County, and the county's Drought Severity and Coverage Index is 185.1 out of 500.
What is Johnson GIS?
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Johnson GIS usually refers to the county's own parcel and zoning mapping system, which Johnson County publishes itself. This page is a separate, free viewer: it draws federal GIS layers — FEMA flood zones, USGS elevation, NLCD land cover and Census boundaries — over the Johnson County boundary, with no login required.
What GIS data is available for Johnson County?
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The Johnson County map loads federal GIS layers directly in your browser: FEMA National Flood Hazard Layer flood zones, USGS 3DEP elevation contours and hillshade, NLCD land cover, Census TIGER school district boundaries, and TIGER ZIP code and county boundary lines.
How do I check flood zones in Johnson County?
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Open the Johnson County map, turn on the FEMA flood zones layer, and zoom in. The National Flood Hazard Layer shows flood insurance rate map zones and floodways. Flood zones only draw once you are zoomed in far enough.
How do I find the coordinates or elevation of a spot in Johnson County?
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Use the inspect tool on the Johnson County map and click any point. It reads back the coordinates, elevation and the layers under your cursor. You can also measure distance and area by drawing a line or polygon.
Data sources for Johnson County, Illinois
Every figure on this page comes from a published government dataset. Each source is listed with its release date so you can check the number or cite it directly.
- American Community Survey 5-year estimates
U.S. Census Bureau · 2020-2024 · population, income, housing, education and poverty figures
- Gazetteer Files
U.S. Census Bureau · 2024 · place coordinates, land area and the county/place/ZIP crosswalk
- TIGER/Line Shapefiles
U.S. Census Bureau · 2024 · county, ZIP Code Tabulation Area and school district boundaries
- National Flood Hazard Layer
Federal Emergency Management Agency · current effective Flood Insurance Rate Maps · flood zones, floodways and base flood elevations
- National Risk Index
Federal Emergency Management Agency · v1.20, December 2025 · county natural hazard risk, expected annual loss, social vulnerability and resilience
- 3D Elevation Program (3DEP)
U.S. Geological Survey · current · elevation contours, shaded relief and point elevations
- National Land Cover Database
Multi-Resolution Land Characteristics Consortium · NLCD 2021 · land cover classes such as developed, forest, crop and water
- Map of Radon Zones
U.S. Environmental Protection Agency · September 2025 · the county radon zone (1, 2 or 3) and its predicted indoor radon potential
- Air Quality Index annual summary by county
U.S. Environmental Protection Agency · 2024 · median, 90th percentile and peak AQI, and days at unhealthy levels, for counties with an EPA monitor
- U.S. Drought Monitor
National Drought Mitigation Center, USDA and NOAA · weekly, current map · the share of county area in each drought category and the Drought Severity and Coverage Index
- ArcGIS basemaps
Esri · current · streets, satellite, topographic and dark gray basemap tiles
Citing this page
GIS Map, “Johnson County, Illinois GIS Map”, https://gismap.land/county/illinois/johnson. Figures from the datasets listed above.
Local notes for Johnson County, IL
Questions and local knowledge from people who know the area. Every note is read before it appears here.