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Rock County
Rock County
County
	Rock County Courthouse
	Seal
	Location within the U.S. state of Wisconsin
	Wisconsin's location within the U.S.
	Coordinates: 42°40′N 89°04′W / 42.67°N 89.07°W
Country	United States
State	Wisconsin
Founded	1839
Named for	Rock River
Seat	Janesville
Largest city	Janesville
Area
• Total	726 sq mi (1,880 km2)
• Land	718 sq mi (1,860 km2)
• Water	8.0 sq mi (21 km2) 1.1%
Population (2020)
• Total	163,687
• Estimate (2023)	164,278
• Density	230/sq mi (87/km2)
Time zone	UTC−6 (Central)
• Summer (DST)	UTC−5 (CDT)
Congressional districts	1st, 2nd
Website	www.co.rock.wi.us

Rock County is a county in the U.S. state of Wisconsin. As of the 2020 census, the population was 163,687.^[1] Its county seat is Janesville.^[2] Rock County comprises the Janesville-Beloit, WI Metropolitan Statistical Area and is included in the Madison-Janesville-Beloit, WI Combined Statistical Area.

History

Rock County was created as a territorial county on December 7, 1836, from Milwaukee County and fully organized February 19, 1839.^[3] The county is named for the Rock River, which bisects the county from north to south.^[4]

Geography

According to the U.S. Census Bureau, the county has a total area of 726 square miles (1,880 km²), of which 718 square miles (1,860 km²) is land and 8.0 square miles (21 km²) (1.1%) is water.^[5]

Cook Memorial Arboretum, a natural area with birding and nature trails, is located northwest of Janesville. It is owned by the Janesville School District.^[6]

Transportation

Major highways

Railroads

Buses

Airport

Southern Wisconsin Regional Airport (KJVL) serves Rock County and the surrounding communities.

Adjacent counties

Green County – west
Dane County – north
Jefferson County – northeast
Walworth County – east
Boone County, Illinois – south
Winnebago County, Illinois – south

Demographics

Historical population
Census	Pop.	%±
1840	1,701	—
1850	20,750	1,119.9%
1860	36,690	76.8%
1870	39,030	6.4%
1880	38,823	−0.5%
1890	43,220	11.3%
1900	51,203	18.5%
1910	55,538	8.5%
1920	66,150	19.1%
1930	74,206	12.2%
1940	80,173	8.0%
1950	92,778	15.7%
1960	113,913	22.8%
1970	131,970	15.9%
1980	139,420	5.6%
1990	139,510	0.1%
2000	152,307	9.2%
2010	160,331	5.3%
2020	163,687	2.1%
U.S. Decennial Census^[7] 1790–1960^[8] 1900–1990^[9] 1990–2000^[10] 2010^[11] 2020^[1]

As of the census of 2020,^[1] the population was 163,687. The population density was 227.9 people per square mile (88.0 people/km²). There were 70,068 housing units at an average density of 97.6 units per square mile (37.7 units/km²). The racial makeup of the county was 81.3% White, 5.1% Black or African American, 1.3% Asian, 0.5% Native American, 4.6% from other races, and 7.2% from two or more races. Ethnically, the population was 9.7% Hispanic or Latino of any race.

As of the census^[12] of 2010, there were 160,331 people residing in the county.

As of the census^[12] of 2000, were 152,307 people, 58,617 households, and 40,387 families residing in the county. The population density was 211 people per square mile (81 people/km²). there were 62,187 housing units at an average density of 86 units per square mile (33 units/km²). The racial makeup of the county was 91.01% white, 4.63% black or African American, 0.28% Native American, 0.78% Asian, 0.04% Pacific Islander, 1.77% from other races, and 1.50% from two or more races. 3.91% of the population were Hispanic or Latino of any race. 32.8% were of German, 13.0% Norwegian, 10.1% Irish, 7.5% English and 5.5% American ancestry.

There were 58,617 households, out of which 33.60% had children under the age of 18 living with them, 53.50% were married couples living together, 10.90% had a female householder with no husband present, and 31.10% were non-families. 25.10% of all households were made up of individuals, and 9.70% had someone living alone who was 65 years of age or older. The average household size was 2.54 and the average family size was 3.03.

In the county, the population was spread out, with 26.50% under the age of 18, 8.60% from 18 to 24, 29.80% from 25 to 44, 22.30% from 45 to 64, and 12.70% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 97.00 males. For every 100 females age 18 and over, there were 94.10 males.

Communities

Cities

Beloit
Brodhead (mostly in Green County)
Edgerton (partly in Dane County)
Evansville
Janesville (County seat)
Milton

Villages

Towns

Census-designated places

Unincorporated communities

Ghost towns/neighborhoods

Politics

United States presidential election results for Rock County, Wisconsin^[13]
Year	Republican		Democratic		Third party(ies)
Year	No.	%	No.	%	No.	%
2024	40,218	45.54%	46,642	52.82%	1,450	1.64%
2020	37,138	43.51%	46,658	54.66%	1,564	1.83%
2016	31,493	41.40%	39,339	51.71%	5,242	6.89%
2012	30,517	37.82%	49,219	61.00%	954	1.18%
2008	27,364	34.56%	50,529	63.82%	1,276	1.61%
2004	33,151	41.19%	46,598	57.90%	730	0.91%
2000	27,467	39.01%	40,472	57.49%	2,465	3.50%
1996	20,096	33.32%	32,450	53.80%	7,774	12.89%
1992	21,942	31.79%	31,154	45.13%	15,929	23.08%
1988	28,178	48.43%	29,576	50.83%	434	0.75%
1984	32,491	54.76%	26,433	44.55%	410	0.69%
1980	30,960	50.60%	24,740	40.44%	5,482	8.96%
1976	28,325	49.04%	28,048	48.56%	1,389	2.40%
1972	30,361	58.03%	21,033	40.20%	925	1.77%
1968	25,229	50.97%	20,567	41.56%	3,697	7.47%
1964	20,372	41.85%	28,257	58.04%	55	0.11%
1960	29,675	60.63%	19,194	39.22%	76	0.16%
1956	28,980	67.42%	13,834	32.18%	173	0.40%
1952	27,837	64.64%	15,183	35.26%	45	0.10%
1948	17,068	50.66%	16,150	47.93%	474	1.41%
1944	18,477	52.23%	16,766	47.39%	133	0.38%
1940	20,141	53.15%	17,543	46.29%	214	0.56%
1936	14,693	43.56%	17,991	53.34%	1,045	3.10%
1932	16,825	56.07%	12,612	42.03%	571	1.90%
1928	21,497	70.75%	8,726	28.72%	161	0.53%
1924	14,815	60.92%	1,453	5.97%	8,052	33.11%
1920	16,152	83.53%	2,447	12.65%	738	3.82%
1916	7,011	61.09%	4,015	34.98%	451	3.93%
1912	4,276	43.21%	3,032	30.64%	2,587	26.14%
1908	7,839	66.81%	3,227	27.50%	668	5.69%
1904	7,972	71.65%	2,348	21.10%	807	7.25%
1900	8,249	69.97%	3,094	26.24%	447	3.79%
1896	8,282	67.46%	3,655	29.77%	340	2.77%
1892	6,052	55.24%	4,231	38.62%	673	6.14%

Since 1988, Rock County has consistently voted for the Democratic candidate in every Presidential election. In 2024, Kamala Harris carried the county by the smallest margin of victory since Michael Dukakis in 1988.

Education

School districts include:^[14]

There is a state-operated school, Wisconsin School for the Blind and Visually Impaired.

Tree cities

Beloit
Clinton
Edgerton
Evansville
Janesville
Milton

References

^ ^a ^b ^c ^d "2020 Decennial Census: Rock County, Wisconsin". data.census.gov. U.S. Census Bureau. Retrieved July 3, 2022.
^ "Find a County". National Association of Counties. Retrieved June 7, 2011.
^ "Wisconsin: Individual County Chronologies". Wisconsin Atlas of Historical County Boundaries. The Newberry Library. 2007. Archived from the original on April 14, 2017. Retrieved August 15, 2015.
^ "Rock County, origin of place name" Dictionary of Wisconsin History.
^ "2010 Census Gazetteer Files". United States Census Bureau. August 22, 2012. Retrieved August 8, 2015.
^ Great Wisconsin Birding & Nature Trail. Cook Memorial Arboretum.
^ "U.S. Decennial Census". United States Census Bureau. Retrieved August 8, 2015.
^ "Historical Census Browser". University of Virginia Library. Retrieved August 8, 2015.
^ Forstall, Richard L., ed. (March 27, 1995). "Population of Counties by Decennial Census: 1900 to 1990". United States Census Bureau. Retrieved August 8, 2015.
^ "Census 2000 PHC-T-4. Ranking Tables for Counties: 1990 and 2000" (PDF). United States Census Bureau. April 2, 2001. Archived (PDF) from the original on October 9, 2022. Retrieved August 8, 2015.
^ "State & County QuickFacts". United States Census Bureau. Archived from the original on February 27, 2016. Retrieved January 23, 2014.
^ ^a ^b "U.S. Census website". United States Census Bureau. Retrieved May 14, 2011.
^ Leip, David. "Dave Leip's Atlas of U.S. Presidential Elections". uselectionatlas.org. Retrieved November 11, 2020.
^ "2020 census - school district reference map: Rock County, WI" (PDF). U.S. Census Bureau. Archived (PDF) from the original on October 9, 2022. Retrieved July 23, 2022. - Text list