County outline
Where Walworth County is located
Area breakdown
Land accounts for 95% of Walworth County’s measured area and water for 5%. Its combined area converts to 1,928.6 square kilometers or approximately 476,564 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 707.455 | 1,832.3 | 452,771.2 |
| Water | 37.177 | 96.288 | 23,793.3 |
| Total | 744.632 | 1,928.588 | 476,564.5 |
How Walworth County compares
By original Census land area, Walworth County ranks #46 of 66 in South Dakota and #1302 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.778 times the South Dakota county-equivalent median of 909.3 square miles. It accounts for 0.9% of the combined county land area in the state.
See the complete South Dakota ranking · What counts as a county equivalent?
Population and density of Walworth County
The Census Bureau estimates that 5,217 people lived in Walworth County on July 1, 2025. That ranks #2,882 of 3,222 county equivalents nationally and #36 of 66 in South Dakota. Since the April 1, 2020 estimates base of 5,317, the population has declined by 100 (−1.9%), compared with +5.5% for South Dakota as a whole.
With 707.5 square miles of land, that is 7.4 people per square mile (2.8 per km²), placing Walworth County #2,748 nationally for density and #26 in South Dakota. The median county equivalent has 47 people per square mile; the South Dakota median is 5.7. Put another way, there are about 87 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 5,291 | 5,255 | 5,259 | 5,256 | 5,244 | 5,217 |
| Change | — | −36 | +4 | −3 | −12 | −27 |
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 Walworth County
6 incorporated places lie at least partly in Walworth County. Together they are home to 4,103 people (78.6%); the other 1,114 (21.4%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Mobridge city, with 3,192 residents in the county. The county seat, Selby city, has 600 residents.
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Mobridge city | 3,192 | −2.2% | 1.96 |
| Selby cityCounty seat | 600 | −2% | 0.712 |
| Java town | 119 | −2.5% | 0.492 |
| Glenham town | 106 | −2.8% | 0.327 |
| Akaska town | 81 | +6.6% | 0.611 |
| Lowry town | 5 | 0% | 0.253 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Walworth County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
Walworth County is not part of any metropolitan or micropolitan statistical area in the Office of Management and Budget’s July 2023 delineation; 1,306 other county equivalents are also outside one. These areas are built around an urban core of at least 10,000 people plus the counties tied to it by commuting, so counties outside them are generally rural.
ZIP codes
7 ZIP Code Tabulation Areas have land in Walworth County; 4 of them have most of their land inside the county, and the others mainly cover neighboring areas.
57420574285745057452574725760157631
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 Walworth County
Walworth County shares a land border with 6 county equivalents. Each of them has more land than Walworth County. The largest neighbor is Corson County (2,469.7 mi²) and the smallest is Campbell County (733.8 mi²). Together with its neighbors, Walworth County forms a block of 9,337.1 mi² of land, of which it holds 7.6%.
| Bordering county equivalent | Land mi² | Size vs. Walworth | Compare |
|---|---|---|---|
| Corson County | 2,469.7 | 3.5× larger | Compare |
| Dewey County | 2,302.4 | 3.3× larger | Compare |
| McPherson County | 1,136.7 | 1.6× larger | Compare |
| Edmunds County | 1,126 | 1.6× larger | Compare |
| Potter County | 861.1 | 1.2× larger | Compare |
| Campbell County | 733.8 | about the same | Compare |
How big is Walworth County compared with U.S. states?
Walworth County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.5 times as much. South Dakota’s county land could hold about 107 areas the size of Walworth County.
Another way to picture it: the same land area would fill a square about 26.6 miles (42.8 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 Walworth County?
Walworth County has more land than 1,920 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 Walworth County at #1,288 nationally by total area, 14 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 5%, compared with a national county-equivalent median of 1.2% — 3.8 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 Walworth County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #1301 | Aurora County, South Dakota | 708.5 | Compare |
| #1302 | Walworth County, South Dakota | 707.5 | This county |
| #1303 | Freeborn County, Minnesota | 707.2 | 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 45.427605, -100.027856. 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: 1,832,300,798 m²; AWATER: 96,288,700 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 Walworth County?
Walworth County, South Dakota has 707.5 square miles (1,832.3 km²) of land and 37.2 square miles of water, for a total area of 744.6 square miles. It ranks #1302 of 3,222 U.S. county equivalents by land area.
Is Walworth County the largest county in South Dakota?
No. Walworth County ranks #46 of 66 in South Dakota by land area. The largest is Meade County, with 3,470.9 square miles of land.
What counties border Walworth County?
Walworth County shares a land border with Campbell County, Potter County, Edmunds County, Dewey County, Corson County, and McPherson County.
What is the population of Walworth County?
The Census Bureau estimates Walworth County had 5,217 residents on July 1, 2025, ranking #2,882 of 3,222 county equivalents. That is 7.4 people per square mile of land.
What is the county seat of Walworth County?
The county seat of Walworth County is Selby.
What cities and towns are in Walworth County?
Walworth County has 6 incorporated places. The most populous five are Mobridge city, Selby city, Java town, Glenham town, and Akaska town; 1,114 residents live outside any incorporated place.
Is Walworth County part of a metropolitan area?
No. Walworth County is outside every metropolitan and micropolitan statistical area in the July 2023 OMB delineation.
How many ZIP codes are in Walworth County?
7 ZIP Code Tabulation Areas have land in Walworth County, and 4 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Walworth County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 1.5 times as much land.
How many acres of land are in Walworth County?
The land measurement converts to approximately 452,771 acres. Including water, total area is approximately 476,564 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.