County outline
Where Union County is located
Area breakdown
Land accounts for 99.4% of Union County’s measured area and water for 0.6%. Its combined area converts to 822.9 square kilometers or approximately 203,352 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 315.957 | 818.325 | 202,212.5 |
| Water | 1.78 | 4.61 | 1,139.2 |
| Total | 317.737 | 822.935 | 203,351.7 |
How Union County compares
By original Census land area, Union County ranks #64 of 67 in Pennsylvania and #2771 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.484 times the Pennsylvania county-equivalent median of 653.3 square miles. It accounts for 0.7% of the combined county land area in the state.
See the complete Pennsylvania ranking · What counts as a county equivalent?
Population and density of Union County
The Census Bureau estimates that 42,313 people lived in Union County on July 1, 2025. That ranks #1,166 of 3,222 county equivalents nationally and #50 of 67 in Pennsylvania. Since the April 1, 2020 estimates base of 42,680, the population has declined by 367 (−0.9%), compared with +0.4% for Pennsylvania as a whole.
With 316 square miles of land, that is 134 people per square mile (52 per km²), placing Union County #826 nationally for density and #36 in Pennsylvania. The median county equivalent has 47 people per square mile; the Pennsylvania median is 137. Put another way, there are about 4.8 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 42,659 | 42,480 | 42,713 | 42,185 | 42,641 | 42,313 |
| Change | — | −179 | +233 | −528 | +456 | −328 |
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
Union County is divided into 14 municipalities and townships. In Pennsylvania, county subdivisions are local governments, and together they cover all of the county’s land and residents.
The most populous is East Buffalo township, with 8,084 residents (19.1% of the county). The largest by land is Hartley township, at 79.6 mi², or 25.2% of the county’s land. The county seat, Lewisburg borough, has 5,226 residents. Among those with at least 1,000 residents in 2020, East Buffalo township grew fastest since then (+9.3%).
| County subdivision | Population 2025 | Since 2020 | Land mi² | Share of county land |
|---|---|---|---|---|
| East Buffalo township | 8,084 | +9.3% | 15.2 | 4.8% |
| Lewisburg boroughCounty seat | 5,226 | +1.3% | 0.973 | 0.3% |
| White Deer township | 4,363 | −1.4% | 46.2 | 14.6% |
| Kelly township | 3,667 | −7.8% | 17.2 | 5.4% |
| Gregg township | 3,594 | −12.2% | 14.9 | 4.7% |
| Buffalo township | 3,546 | −1.2% | 30.1 | 9.5% |
| Mifflinburg borough | 3,436 | −1.3% | 1.804 | 0.6% |
| West Buffalo township | 2,852 | −1.5% | 38.3 | 12.1% |
| Limestone township | 1,739 | −0.8% | 20.6 | 6.5% |
| Hartley township | 1,717 | −1.9% | 79.6 | 25.2% |
| Union township | 1,612 | −1.3% | 11.2 | 3.5% |
| Lewis township | 1,461 | −1.4% | 38.7 | 12.3% |
| New Berlin borough | 771 | −3.1% | 0.388 | 0.1% |
| Hartleton borough | 245 | −2% | 0.908 | 0.3% |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each subdivision inside Union County. Land: 2026 Census Gazetteer. How communities are listed.
Metropolitan area
Union County is a central county of the Lewisburg, PA Micropolitan Statistical Area. Union County is the area’s only county equivalent, so the micro area has the same 316 square miles of land. By combined land it ranks #518 of 542 micropolitan areas, and #298 by population. It belongs to the Bloomsburg-Berwick-Sunbury, PA Combined Statistical Area.
ZIP codes
14 ZIP Code Tabulation Areas have land in Union County; 11 of them have most of their land inside the county, and the others mainly cover neighboring areas.
1781017829178351783717844178451785517856178701788017885178861788717889
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 6 county equivalents. Each of them has more land than Union County. The largest neighbor is Lycoming County (1,228.9 mi²) and the smallest is Snyder County (328.8 mi²). Together with its neighbors, Union County forms a block of 4,739.5 mi² of land, of which it holds 6.7%.
| Bordering county equivalent | Land mi² | Size vs. Union | Compare |
|---|---|---|---|
| Lycoming County | 1,228.9 | 3.9× larger | Compare |
| Centre County | 1,107.3 | 3.5× larger | Compare |
| Clinton County | 889.8 | 2.8× larger | Compare |
| Northumberland County | 457.7 | 1.4× larger | Compare |
| Mifflin County | 411 | 1.3× larger | Compare |
| Snyder County | 328.8 | about the same | Compare |
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 3.3 times as much. Pennsylvania’s county land could hold about 142 areas the size of Union County.
Another way to picture it: the same land area would fill a square about 17.8 miles (28.6 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 451 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 #2,809 nationally by total area, 38 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 0.6%, compared with a national county-equivalent median of 1.2% — 0.6 percentage points lower. 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 |
|---|---|---|---|
| #2770 | Rockcastle County, Kentucky | 316.6 | Compare |
| #2771 | Union County, Pennsylvania | 316 | This county |
| #2772 | Isle of Wight County, Virginia | 315.7 | 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 40.962179, -77.055475. 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: 818,323,648 m²; AWATER: 4,611,410 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, Pennsylvania has 316 square miles (818.3 km²) of land and 1.78 square miles of water, for a total area of 317.7 square miles. It ranks #2771 of 3,222 U.S. county equivalents by land area.
Is Union County the largest county in Pennsylvania?
No. Union County ranks #64 of 67 in Pennsylvania by land area. The largest is Lycoming County, with 1,228.9 square miles of land.
What counties border Union County?
Union County shares a land border with Snyder County, Northumberland County, Centre County, Lycoming County, Mifflin County, and Clinton County.
What is the population of Union County?
The Census Bureau estimates Union County had 42,313 residents on July 1, 2025, ranking #1,166 of 3,222 county equivalents. That is 134 people per square mile of land.
What is the county seat of Union County?
The county seat of Union County is Lewisburg.
What cities and towns are in Union County?
Union County has 14 county subdivisions (cities, towns and townships). The most populous five are East Buffalo township, Lewisburg borough, White Deer township, Kelly township, and Gregg township.
Is Union County part of a metropolitan area?
Yes. It is a central county of the Lewisburg, PA Micropolitan Statistical Area.
How many ZIP codes are in Union County?
14 ZIP Code Tabulation Areas have land in Union County, and 11 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 less land than every state. Rhode Island, the smallest, has 3.3 times as much land.
How many acres of land are in Union County?
The land measurement converts to approximately 202,212 acres. Including water, total area is approximately 203,352 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.