Clay County area

Population and density of Clay County

The Census Bureau estimates that 15,031 people lived in Clay County on July 1, 2025. That ranks #2,163 of 3,222 county equivalents nationally and #14 of 66 in South Dakota. Since the April 1, 2020 estimates base of 14,973, the population has grown by 58 (+0.4%), compared with +5.5% for South Dakota as a whole.

With 412 square miles of land, that is 36 people per square mile (14 per km²), placing Clay County #1,840 nationally for density and #10 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 18 acres of land per resident.

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 Clay County

3 incorporated places lie at least partly in Clay County. Together they are home to 12,253 people (81.5%); the other 2,778 (18.5%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Vermillion city, with 11,720 residents in the county.

Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Clay County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.

Metropolitan area

Clay County is a central county of the Vermillion, SD Micropolitan Statistical Area. Clay County is the area’s only county equivalent, so the micro area has the same 412 square miles of land. By combined land it ranks #475 of 542 micropolitan areas, and #536 by population.

ZIP codes

8 ZIP Code Tabulation Areas have land in Clay County; 3 of them have most of their land inside the county, and the others mainly cover neighboring areas.

5700457010570145703157037570695707257073

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 Clay County

Clay County shares a land border with 6 county equivalents, including 2 in Nebraska. Each of them has more land than Clay County. The largest neighbor is Cedar County (740.2 mi²) and the smallest is Union County (462 mi²). Together with its neighbors, Clay County forms a block of 3,805.4 mi² of land, of which it holds 10.8%.

How big is Clay County compared with U.S. states?

Clay County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 2.5 times as much. South Dakota’s county land could hold about 184 areas the size of Clay County.

Another way to picture it: the same land area would fill a square about 20.3 miles (32.7 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 Clay County?

Clay County has more land than 767 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 Clay County at #2,504 nationally by total area, 49 places farther from the top than its land rank. Other county equivalents gain more area when their water measurements are included.

Its water share is 1.3%, compared with a national county-equivalent median of 1.2% — 0.1 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 Clay County in the national ranking. They can be in different states and are not necessarily geographic neighbors.

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.