County Maps US

Union County, South Dakota

A county in South Dakota, ranked 13 of 66 by population.

CountyFIPS 46127

Within South Dakota
Union County, highlighted, with the areas around it. Boundaries generalised from the 2025 Census cartographic boundary file; neighbour fills carry no data. The dot marks Elk Point, the county seat, located via the 2025 Census Gazetteer.

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Population
17,402
+547 (+3.2%) since 2020
Land area
460.8
square miles. A further 1.4% of the total area is water
Population density
37.8
people per square mile, computed rather than published
County seat
Elk Point
Seat of county government.
Established
1862
163 years ago
Largest city
North Sioux City city
Population 3,036.

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; Wikidata (CC0), Wikidata. Retrieved 30 August 2026.

Satellite view

Aerial imagery of Union County with its boundary drawn on top. A map shows you the shape; this shows you what is inside it, and which side of the line a place falls on.

Aerial view of Union County, South Dakota from the USGS National Map, with its boundary outlined
Imagery: USGS National Map, USGS Imagery Only, public domain, requested from USGS by your browser when you reach this point on the page, at 399 by 800 pixels. The boundary is the 2025 Census cartographic boundary file, reprojected to Web Mercator to match the imagery. You can also open the USGS National Map viewer.

Where Union County ranks

Position among the 66 counties of South Dakota, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.

MeasureValueIn South DakotaNationally
Population17,40213th of 661,962nd of 3,144
Land area460.8 sq mi62nd of 662,227th of 3,144
Population density37.8 per sq mi8th of 661,721st of 3,144
Median household income$89,6362nd of 66311th of 3,143

Full data for Union County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population17,402Vintage 2025 Population Estimates
Population in 202016,855Vintage 2025 Population Estimates
2020 estimates base?16,813Vintage 2025 Population Estimates
Land area460.8 sq mi2025 Gazetteer Files
Water area6.4 sq mi2025 Gazetteer Files
Total area467.1 sq mi2025 Gazetteer Files
Population density?37.8 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$89,636American Community Survey 2020-2024 5-Year Estimates
Median home value$301,100American Community Survey 2020-2024 5-Year Estimates
Median age41.5American Community Survey 2020-2024 5-Year Estimates
Households7,310American Community Survey 2020-2024 5-Year Estimates
Housing units7,588American Community Survey 2020-2024 5-Year Estimates

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; US Census Bureau, American Community Survey, American Community Survey 2020-2024 5-Year Estimates, released 29 January 2026. Population density is computed here, not published: it divides the Vintage 2025 population estimate by the 2025 Gazetteer land area, which are two different Census products. Retrieved 30 August 2026.

How the population changed

The Census Bureau publishes the components behind an estimate, not just the total. For the year to July 2025:

Births minus deaths
+104
247 births, 143 deaths
Net migration
-76
More people moved out than moved in.

Source: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026. Retrieved 30 August 2026.

The 7 areas bordering Union County

Ordered by the length of the border actually shared, which the Census Bureau publishes in its county adjacency file and which no other county reference presents.

Bordering areaStateShared borderPopulation
Plymouth CountyIowa55 mi25,697
Clay CountySouth Dakota26 mi15,031
Sioux CountyIowa21 mi36,774
Dixon CountyNebraska20 mi5,602
Lincoln CountySouth Dakota18 mi77,145
Dakota CountyNebraska12 mi21,687
Woodbury CountyIowa8.9 mi106,649

Source: US Census Bureau, County Adjacency File, 2025 County Adjacency File, released 15 September 2025. Retrieved 30 August 2026.

All 66 counties of South Dakota

Open the interactive South Dakota county map, or jump straight to any of them.

Data on this page last rebuilt 30 August 2026. How these figures are produced.