County outline
Where Union County is located
Area breakdown
Land accounts for 98.5% of Union County’s measured area and water for 1.5%. Its combined area converts to 2,733.3 square kilometers or approximately 675,407 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 1,039.067 | 2,691.171 | 665,002.9 |
| Water | 16.256 | 42.103 | 10,403.8 |
| Total | 1,055.323 | 2,733.274 | 675,406.7 |
How Union County compares
By original Census land area, Union County ranks #1 of 75 in Arkansas and #635 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 1.605 times the Arkansas county-equivalent median of 647.2 square miles. It accounts for 2% of the combined county land area in the state.
See the complete Arkansas ranking · What counts as a county equivalent?
Population and density of Union County
The Census Bureau estimates that 36,926 people lived in Union County on July 1, 2025. That ranks #1,298 of 3,222 county equivalents nationally and #21 of 75 in Arkansas. Since the April 1, 2020 estimates base of 39,059, the population has declined by 2,133 (−5.5%), compared with +3.4% for Arkansas as a whole.
With 1,039.1 square miles of land, that is 36 people per square mile (14 per km²), placing Union County #1,862 nationally for density and #26 in Arkansas. The median county equivalent has 47 people per square mile; the Arkansas median is 28. Put another way, there are about 18 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 38,942 | 38,312 | 37,856 | 37,413 | 37,121 | 36,926 |
| Change | — | −630 | −456 | −443 | −292 | −195 |
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 Union County
8 incorporated places lie at least partly in Union County. Together they are home to 20,705 people (56.1%); the other 16,221 (43.9%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is El Dorado city, with 16,609 residents in the county.
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| El Dorado cityCounty seat | 16,609 | −6.5% | 16.2 |
| Smackover city | 1,584 | −2.9% | 4.349 |
| Norphlet city | 717 | −5.8% | 2.031 |
| Junction City city | 476 | −5.6% | 1.136 |
| Huttig city | 427 | −5.9% | 2.979 |
| Calion city | 409 | −5.1% | 1.072 |
| Strong city | 400 | −4.3% | 1.597 |
| Felsenthal town | 83 | −1.2% | 1.476 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Union County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
Union County is a central county of the El Dorado, AR Micropolitan Statistical Area. Union County is the area’s only county equivalent, so the micro area has the same 1,039.1 square miles of land. By combined land it ranks #171 of 542 micropolitan areas, and #367 by population.
ZIP codes
10 ZIP Code Tabulation Areas have land in Union County; 8 of them have most of their land inside the county, and the others mainly cover neighboring areas.
71724717307174771749717537175871759717627176471765
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 Union County
Union County shares a land border with 7 county equivalents, including 2 in Louisiana. It has more land than every one of them. The largest neighbor is Ashley County (925.5 mi²) and the smallest is Calhoun County (628.6 mi²). Together with its neighbors, Union County forms a block of 6,372.8 mi² of land, of which it holds 16.3%.
| Bordering county equivalent | Land mi² | Size vs. Union | Compare |
|---|---|---|---|
| Ashley County | 925.5 | 1.1× smaller | Compare |
| Union ParishLouisiana | 876.9 | 1.2× smaller | Compare |
| Columbia County | 766.1 | 1.4× smaller | Compare |
| Claiborne ParishLouisiana | 754.8 | 1.4× smaller | Compare |
| Ouachita County | 732.7 | 1.4× smaller | Compare |
| Bradley County | 649.2 | 1.6× smaller | Compare |
| Calhoun County | 628.6 | 1.7× smaller | Compare |
How big is Union County compared with U.S. states?
Union County has more land than 1 of the 50 states. It is about 1 times the land area of Rhode Island (1,033.9 mi²), while Delaware, the next larger state, has 1.9 times as much land (1,948.6 mi²). Arkansas’s county land could hold about 50 areas the size of Union County.
Another way to picture it: the same land area would fill a square about 32.2 miles (51.9 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 Union County?
Union County has more land than 2,587 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 Union County at #716 nationally by total area, 81 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 1.5%, compared with a national county-equivalent median of 1.2% — 0.4 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 Union County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #634 | Live Oak County, Texas | 1,039.7 | Compare |
| #635 | Union County, Arkansas | 1,039.1 | This county |
| #636 | Harper County, Oklahoma | 1,038.6 | 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 33.168219, -92.598145. 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: 2,691,170,075 m²; AWATER: 42,102,267 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 Union County?
Union County, Arkansas has 1,039.1 square miles (2,691.2 km²) of land and 16.3 square miles of water, for a total area of 1,055.3 square miles. It ranks #635 of 3,222 U.S. county equivalents by land area.
Is Union County the largest county in Arkansas?
Yes. Union County has the most land of the 75 county equivalents in Arkansas.
What counties border Union County?
Union County shares a land border with Union Parish, Louisiana, Columbia County, Ouachita County, Bradley County, Calhoun County, Claiborne Parish, Louisiana, and Ashley County.
What is the population of Union County?
The Census Bureau estimates Union County had 36,926 residents on July 1, 2025, ranking #1,298 of 3,222 county equivalents. That is 36 people per square mile of land.
What is the county seat of Union County?
The county seat of Union County is El Dorado.
What cities and towns are in Union County?
Union County has 8 incorporated places. The most populous five are El Dorado city, Smackover city, Norphlet city, Junction City city, and Huttig city; 16,221 residents live outside any incorporated place.
Is Union County part of a metropolitan area?
Yes. It is a central county of the El Dorado, AR Micropolitan Statistical Area.
How many ZIP codes are in Union County?
10 ZIP Code Tabulation Areas have land in Union County, and 8 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Union County compare with U.S. states?
It has more land than 1 of the 50 states, including Rhode Island (1,033.9 square miles of land).
How many acres of land are in Union County?
The land measurement converts to approximately 665,003 acres. Including water, total area is approximately 675,407 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.