County outline
Where Jefferson County is located
Area breakdown
Land accounts for 95.5% of Jefferson County’s measured area and water for 4.5%. Its combined area converts to 1,509.3 square kilometers or approximately 372,955 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 556.494 | 1,441.313 | 356,156.2 |
| Water | 26.248 | 67.982 | 16,798.7 |
| Total | 582.742 | 1,509.295 | 372,954.9 |
How Jefferson County compares
By original Census land area, Jefferson County ranks #53 of 72 in Wisconsin and #1863 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.739 times the Wisconsin county-equivalent median of 753 square miles. It accounts for 1% of the combined county land area in the state.
See the complete Wisconsin ranking · What counts as a county equivalent?
Population and density of Jefferson County
The Census Bureau estimates that 86,505 people lived in Jefferson County on July 1, 2025. That ranks #693 of 3,222 county equivalents nationally and #20 of 72 in Wisconsin. Since the April 1, 2020 estimates base of 86,171, the population has grown by 334 (+0.4%), compared with +1.3% for Wisconsin as a whole.
With 556.5 square miles of land, that is 155 people per square mile (60 per km²), placing Jefferson County #758 nationally for density and #17 in Wisconsin. The median county equivalent has 47 people per square mile; the Wisconsin median is 51. Put another way, there are about 4.1 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 86,219 | 85,830 | 85,883 | 86,086 | 86,540 | 86,505 |
| Change | — | −389 | +53 | +203 | +454 | −35 |
U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.
Cities and towns in Jefferson County
Jefferson County is divided into 27 cities and towns. In Wisconsin, county subdivisions are local governments, and together they cover all of the county’s land and residents.
The most populous is Watertown city, with 14,485 residents (16.7% of the county). The largest by land is Jefferson town, at 42.5 mi², or 7.6% of the county’s land. The county seat, Jefferson city, has 7,814 residents. Among those with at least 1,000 residents in 2020, Lake Mills city grew fastest since then (+6.9%).
| County subdivision | Population 2025 | Since 2020 | Land mi² | Share of county land |
|---|---|---|---|---|
| Watertown city | 14,485 | −1.4% | 7.998 | 1.4% |
| Fort Atkinson city | 12,388 | −1.7% | 5.851 | 1.1% |
| Jefferson cityCounty seat | 7,814 | +0.3% | 5.832 | 1% |
| Lake Mills city | 6,655 | +6.9% | 4.188 | 0.8% |
| Ixonia town | 5,083 | −1% | 35.8 | 6.4% |
| Whitewater city | 4,481 | +1.3% | 2.856 | 0.5% |
| Koshkonong town | 3,776 | +1.1% | 41.2 | 7.4% |
| Waterloo city | 3,600 | +3.3% | 3.794 | 0.7% |
| Johnson Creek village | 3,435 | +3.3% | 3.084 | 0.6% |
| Oakland town | 3,215 | −0.2% | 34.6 | 6.2% |
| Sullivan town | 2,318 | +1.2% | 34.9 | 6.3% |
| Lake Mills town | 2,206 | +0.5% | 30.3 | 5.4% |
| Jefferson townCounty seat | 2,060 | −0.3% | 42.5 | 7.6% |
| Concord town | 1,964 | −1.2% | 35.7 | 6.4% |
| Watertown town | 1,938 | +1% | 37.4 | 6.7% |
Show the other 12 subdivisions
| Name | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Palmyra village | 1,720 | −0.6% | 2.291 |
| Farmington town | 1,398 | −0.9% | 35.1 |
| Aztalan town | 1,373 | −0.2% | 24.1 |
| Palmyra town | 1,230 | +1.6% | 33.6 |
| Milford town | 1,108 | −0.2% | 33.8 |
| Hebron town | 1,054 | +0.6% | 28.9 |
| Waterloo town | 876 | +0.3% | 32.3 |
| Sumner town | 829 | −2% | 16.3 |
| Cold Spring town | 728 | −0.1% | 22.5 |
| Sullivan village | 663 | +1.5% | 1.136 |
| Cambridge village | 108 | +4.9% | 0.162 |
| Lac La Belle village | 0 | — | 0.298 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each subdivision inside Jefferson County. Land: 2026 Census Gazetteer. How communities are listed.
Metropolitan area
Jefferson County is a central county of the Watertown-Fort Atkinson, WI Micropolitan Statistical Area. Jefferson County is the area’s only county equivalent, so the micro area has the same 556.5 square miles of land. By combined land it ranks #391 of 542 micropolitan areas, and #57 by population. It belongs to the Milwaukee-Racine-Waukesha, WI Combined Statistical Area.
ZIP codes
19 ZIP Code Tabulation Areas have land in Jefferson County; 10 of them have most of their land inside the county, and the others mainly cover neighboring areas.
53036530385306653094530985311853119531375315653178531905352353534535385354953551535595356353594
ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.
Counties bordering Jefferson County
Jefferson County shares a land border with 5 county equivalents. It has more land than 2 of them. The largest neighbor is Dane County (1,196.5 mi²) and the smallest is Waukesha County (549.7 mi²). Together with its neighbors, Jefferson County forms a block of 4,452 mi² of land, of which it holds 12.5%.
| Bordering county equivalent | Land mi² | Size vs. Jefferson | Compare |
|---|---|---|---|
| Dane County | 1,196.5 | 2.2× larger | Compare |
| Dodge County | 875.7 | 1.6× larger | Compare |
| Rock County | 718.2 | 1.3× larger | Compare |
| Walworth County | 555.4 | about the same | Compare |
| Waukesha County | 549.7 | about the same | Compare |
How big is Jefferson County compared with U.S. states?
Jefferson County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.9 times as much. Wisconsin’s county land could hold about 97 areas the size of Jefferson County.
Another way to picture it: the same land area would fill a square about 23.6 miles (38 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.
State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.
What stands out about Jefferson County?
Jefferson County has more land than 1,359 of the other 3,221 county equivalents in the dataset.
A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.
Does including water change its rank?
Using land plus water places Jefferson County at #1,816 nationally by total area, 47 places closer to the top than its land rank. The water assigned to this geography moves it ahead of some county equivalents with more land.
Its water share is 4.5%, compared with a national county-equivalent median of 1.2% — 3.3 percentage points higher. This describes the statistical geography’s land/water mix, not flood exposure or developable land.
Closest positions in the national land ranking
These entries sit immediately beside Jefferson County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #1862 | Cass County, Nebraska | 556.9 | Compare |
| #1863 | Jefferson County, Wisconsin | 556.5 | This county |
| #1864 | Crawford County, Michigan | 556.4 | Compare |
Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.
Representative coordinates
The Census internal point is 43.013804, -88.773985. It represents a location inside the geography; it is not necessarily the centroid or the address of a courthouse.
Source and precision
U.S. Census Bureau, 2026 Gazetteer Files, Counties. Original ALAND: 1,441,311,741 m²; AWATER: 67,982,465 m². Rankings use ALAND; exact ties use ascending GEOID. Tables preserve Census-published square miles to three decimals, with conversions based on those values.
Common questions
How big is Jefferson County?
Jefferson County, Wisconsin has 556.5 square miles (1,441.3 km²) of land and 26.2 square miles of water, for a total area of 582.7 square miles. It ranks #1863 of 3,222 U.S. county equivalents by land area.
Is Jefferson County the largest county in Wisconsin?
No. Jefferson County ranks #53 of 72 in Wisconsin by land area. The largest is Marathon County, with 1,545.2 square miles of land.
What counties border Jefferson County?
Jefferson County shares a land border with Waukesha County, Dane County, Dodge County, Walworth County, and Rock County.
What is the population of Jefferson County?
The Census Bureau estimates Jefferson County had 86,505 residents on July 1, 2025, ranking #693 of 3,222 county equivalents. That is 155 people per square mile of land.
What is the county seat of Jefferson County?
The county seat of Jefferson County is Jefferson.
What cities and towns are in Jefferson County?
Jefferson County has 27 county subdivisions (cities, towns and townships). The most populous five are Watertown city, Fort Atkinson city, Jefferson city, Lake Mills city, and Ixonia town.
Is Jefferson County part of a metropolitan area?
Yes. It is a central county of the Watertown-Fort Atkinson, WI Micropolitan Statistical Area.
How many ZIP codes are in Jefferson County?
19 ZIP Code Tabulation Areas have land in Jefferson County, and 10 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Jefferson County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 1.9 times as much land.
How many acres of land are in Jefferson County?
The land measurement converts to approximately 356,156 acres. Including water, total area is approximately 372,955 acres. One square mile equals 640 acres.
Why might another source show a different area?
Check whether it reports land or total area, its Census vintage, and its rounding. Our guide explains how to reconcile county area figures.
Can this establish a property boundary?
No. Statistical measurements and generalized maps do not establish property lines. Consult the relevant local surveying or land-records authority.