Rock County is a county in the U.S. state of Wisconsin. As of the 2020 census, the population was 163,687. Its county seat is Janesville. 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. The county is named for the Rock River, which bisects the county from north to south.

Geography

According to the U.S. Census Bureau, the county has a total area of 726 sqmi, of which 718 sqmi is land and 8.0 sqmi (1.1%) is water. Cook Memorial Arboretum, a natural area with birding and nature trails, is located northwest of Janesville. It is owned by the Janesville School District.

Transportation

Major highways

Railroads

Buses

Airport

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

Adjacent counties

Demographics

As of the census of 2020, the population was 163,687. The population density was 227.9 /mi2. There were 70,068 housing units at an average density of 97.6 /mi2. 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 of 2010, there were 160,331 people residing in the county. As of the census of 2000, were 152,307 people, 58,617 households, and 40,387 families residing in the county. The population density was 211 /mi2. there were 62,187 housing units at an average density of 86 /mi2. 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

Villages

Towns

Census-designated places

Unincorporated communities

Ghost towns/neighborhoods

Politics

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

Tree cities