County Maps US

Rock County, Wisconsin

A county in Wisconsin, ranked 9 of 72 by population.

CountyFIPS 55105

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

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Population
166,472
+2,709 (+1.7%) since 2020
Land area
718.2
square miles. A further 1.1% of the total area is water
Population density
232
people per square mile, computed rather than published
County seat
Janesville
Seat of county government.
Established
1836
189 years ago
Largest city
Janesville city
Population 66,929.

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 Rock 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 Rock County, Wisconsin 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 800 by 668 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 Rock County ranks

Position among the 72 counties of Wisconsin, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.

MeasureValueIn WisconsinNationally
Population166,4729th of 72424th of 3,144
Land area718.2 sq mi41st of 721,251st of 3,144
Population density232 per sq mi12th of 72520th of 3,144
Median household income$75,67325th of 72797th of 3,143

Full data for Rock County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population166,472Vintage 2025 Population Estimates
Population in 2020163,763Vintage 2025 Population Estimates
2020 estimates base?163,684Vintage 2025 Population Estimates
Land area718.2 sq mi2025 Gazetteer Files
Water area8.0 sq mi2025 Gazetteer Files
Total area726.2 sq mi2025 Gazetteer Files
Population density?232 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$75,673American Community Survey 2020-2024 5-Year Estimates
Median home value$231,600American Community Survey 2020-2024 5-Year Estimates
Median age40.3American Community Survey 2020-2024 5-Year Estimates
Households67,201American Community Survey 2020-2024 5-Year Estimates
Housing units71,109American 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
+72
1,797 births, 1,725 deaths
Net migration
+731
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 Rock 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
Walworth CountyWisconsin24 mi106,127
Green CountyWisconsin24 mi37,227
Winnebago CountyIllinois22 mi283,674
Dane CountyWisconsin18 mi590,375
Jefferson CountyWisconsin12 mi86,505
Boone CountyIllinois8.4 mi53,568

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

All 72 counties of Wisconsin

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

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