County Maps US

Johnson County, Illinois

A county in Illinois, ranked 77 of 102 by population.

CountyFIPS 17087

Within Illinois
Johnson County, highlighted, with the areas around it. Boundaries generalised from the 2025 Census cartographic boundary file; neighbour fills carry no data. The dot marks Vienna, the county seat, located via the 2025 Census Gazetteer.

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Population
13,363
+46 (+0.3%) since 2020
Land area
343.7
square miles. A further 1.4% of the total area is water
Population density
38.9
people per square mile, computed rather than published
County seat
Vienna
Seat of county government.
Established
1812
213 years ago
Largest city
Vienna city
Population 1,352.

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; Wikidata (CC0), Wikidata. Retrieved 30 August 2026.

Satellite view

Aerial imagery of Johnson County with its boundary drawn on top. A map shows you the shape; this shows you what is inside it, and which side of the line a place falls on.

Aerial view of Johnson County, Illinois from the USGS National Map, with its boundary outlined
Imagery: USGS National Map, USGS Imagery Only, public domain, requested from USGS by your browser when you reach this point on the page, at 708 by 800 pixels. The boundary is the 2025 Census cartographic boundary file, reprojected to Web Mercator to match the imagery. You can also open the USGS National Map viewer.

Where Johnson County ranks

Position among the 102 counties of Illinois, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.

MeasureValueIn IllinoisNationally
Population13,36377th of 1022,198th of 3,144
Land area343.7 sq mi85th of 1022,698th of 3,144
Population density38.9 per sq mi59th of 1021,693rd of 3,144
Median household income$62,52872nd of 1021,844th of 3,143

Full data for Johnson County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population13,363Vintage 2025 Population Estimates
Population in 202013,317Vintage 2025 Population Estimates
2020 estimates base?13,304Vintage 2025 Population Estimates
Land area343.7 sq mi2025 Gazetteer Files
Water area4.9 sq mi2025 Gazetteer Files
Total area348.7 sq mi2025 Gazetteer Files
Population density?38.9 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$62,528American Community Survey 2020-2024 5-Year Estimates
Median home value$160,500American Community Survey 2020-2024 5-Year Estimates
Median age41.4American Community Survey 2020-2024 5-Year Estimates
Households4,101American Community Survey 2020-2024 5-Year Estimates
Housing units5,541American Community Survey 2020-2024 5-Year Estimates

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; US Census Bureau, American Community Survey, American Community Survey 2020-2024 5-Year Estimates, released 29 January 2026. Population density is computed here, not published: it divides the Vintage 2025 population estimate by the 2025 Gazetteer land area, which are two different Census products. Retrieved 30 August 2026.

How the population changed

The Census Bureau publishes the components behind an estimate, not just the total. For the year to July 2025:

Births minus deaths
-41
96 births, 137 deaths
Net migration
+58
More people moved in than moved out.

Source: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026. Retrieved 30 August 2026.

The 6 areas bordering Johnson County

Ordered by the length of the border actually shared, which the Census Bureau publishes in its county adjacency file and which no other county reference presents.

Bordering areaStateShared borderPopulation
Union CountyIllinois18 mi16,656
Williamson CountyIllinois18 mi67,225
Pope CountyIllinois18 mi3,672
Massac CountyIllinois15 mi13,502
Pulaski CountyIllinois11 mi4,820
Saline CountyIllinois79 ft22,772

Source: US Census Bureau, County Adjacency File, 2025 County Adjacency File, released 15 September 2025. Retrieved 30 August 2026.

All 102 counties of Illinois

Open the interactive Illinois county map, or jump straight to any of them.

Data on this page last rebuilt 30 August 2026. How these figures are produced.