County · code 55105
Rock CountyWisconsin
Rock County is in Wisconsin and has its county seat in Janesville. The county was created in 1836.
- Founded1836
- County seatJanesville
- Land area718 sq mi + 8 sq mi water
- Population163,687 2020 Census
- Parcels mapped39,678 checked 14 October 2026
Where it is
Rock on the map of Wisconsin
Wisconsin has 72 counties and county equivalents, each with its own records office. Shapes with a page are links.
History
Formed in 1836 from Milwaukee County and Racine County
An old deed may name a county that no longer exists, or a boundary that has since moved.
Rock County was created by Wisconsin Territory from Milwaukee and Racine on December 7, 1836, but was not fully organized and was attached to Racine for judicial purposes. In 1838, Rock County gained additional territory when Non-County Area 2 was eliminated. The county became fully organized on February 13, 1839, when it was detached from Racine. Rock County became a county in the state of Wisconsin on May 29, 1848.
- 1836Rock County created Rock created by Wisconsin Territory from Milwaukee; Rock not fully organized, attached to Racine "for judicial purposes." · Wis. Terr. Laws 1836, no. 28, secs. 2, 13/pp. 92, 94
- 1838Gained territory Rock gained all of Non-County Area 2; Non-County Area 2 eliminated. · Wis. Terr. Laws 1838, spec. sess., no. 5, sec. 1/p. 539
- 1839Changed Rock fully organized, detached from Racine. · Wis. Terr. Laws 1838-1839, loc. acts, no. 22, secs. 1, 4/pp. 25-26
- 1848Became part of Wisconsin Rock became a county in the state of Wisconsin. · U.S. Stat., vol. 9, ch. 89 [1846]/pp. 56-58, and ch. 50 [1848]/pp. 233-235; Van Zandt, 128, 130
Land and parcels
What the maps cover in Rock
Who publishes each layer, how good it is, and when we last checked.
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Parcels Good enough
Lot lines and tax-map numbers for 39,678 parcels from Rock County. Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
checked 14 October 2026 -
Address points Missing
No public address points layer found for Rock County yet.
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Buildings Reference
Roof outlines traced from aerial imagery from FEMA Response Geospatial Office with Oak Ridge National Laboratory (ORNL). Good for seeing what is on a lot; not accurate enough to set a fence from.
checked 18 October 2026
- Official
- from the office that keeps the record
- Good enough
- a reliable statewide or national copy
- Fallback
- a guide only; check the official record
- Missing
- nothing public found yet
People and land
Rock by the Census
Source: US Census Bureau, 2020 Census; US Census Bureau, 2020 Gazetteer Files. Not endorsed or certified by the Census Bureau.
Rules and offices
Rock County's official site
We have found the county's site but not its offices yet; start there.
County government
- County government
The official website of Rock County.
See your own lot on these maps
Open Rock County on Parcel Chart's free map and click your parcel. Save it with a free account; the full record of your place (site map, projects, documents) is Pro, in early access.
Questions
Common questions about Rock County
- When was Rock County founded?
- Rock County was founded in 1836, formed from Milwaukee County and Racine County.
- What is the county seat of Rock County?
- The county seat of Rock County is Janesville.
- Is there an online parcel map for Rock County?
- Yes. Rock County publishes a parcel map of 39,678 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
- Has Rock County's boundary or name changed?
- Rock County was created in 1836 from Milwaukee County and Racine County. Since then the Atlas of Historical County Boundaries records 3 later changes, chiefly involving Racine County.
- Is my lot in a flood zone?
- We do not have flood maps for Rock County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.
Nearby