Union County area

Population and density of Union County

The Census Bureau estimates that 73,446 people lived in Union County on July 1, 2025. That ranks #771 of 3,222 county equivalents nationally and #34 of 88 in Ohio. Since the April 1, 2020 estimates base of 62,795, the population has grown by 10,651 (+17%), compared with +0.9% for Ohio as a whole.

With 431.7 square miles of land, that is 170 people per square mile (66 per km²), placing Union County #705 nationally for density and #30 in Ohio. The median county equivalent has 47 people per square mile; the Ohio median is 120. Put another way, there are about 3.8 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 Union County

7 incorporated places lie at least partly in Union County. Together they are home to 39,335 people (53.6%); the other 34,111 (46.4%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Marysville city, with 30,190 residents in the county. By land, Dublin city is the largest at 25.1 mi² across all its counties. Among places with at least 1,000 residents in 2020, Richwood village grew fastest since then (+19%).

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 an outlying county of the Columbus, OH Metropolitan Statistical Area. Its 10 county equivalents have 2,242,028 residents on 4,797.5 square miles of land; Union County accounts for 9% of the land and 3.3% of the residents. By combined land it ranks #55 of 393 metropolitan areas, and #32 by population. It belongs to the Columbus-Marion-Zanesville, OH Combined Statistical Area.

ZIP codes

21 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.

430074301543016430174302943036430404304543060430614306443067430774308443302433194334043342433444334543358

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. It has more land than 2 of them. The largest neighbor is Franklin County (532.4 mi²) and the smallest is Marion County (403.8 mi²). Together with its neighbors, Union County forms a block of 3,635.6 mi² of land, of which it holds 11.9%.

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

Union County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 2.4 times as much. Ohio’s county land could hold about 95 areas the size of Union County.

Another way to picture it: the same land area would fill a square about 20.8 miles (33.4 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 871 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 #2,402 nationally by total area, 51 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 1.2%, compared with a national county-equivalent median of 1.2%. The two percentages are within 0.1 percentage points of each other. 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.

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.