County outline
Where Montgomery County is located
Area breakdown
Land accounts for 99.4% of Montgomery County’s measured area and water for 0.6%. Its combined area converts to 1,202.4 square kilometers or approximately 297,117 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 461.352 | 1,194.896 | 295,265.3 |
| Water | 2.893 | 7.493 | 1,851.5 |
| Total | 464.245 | 1,202.389 | 297,116.8 |
How Montgomery County compares
By original Census land area, Montgomery County ranks #37 of 88 in Ohio and #2225 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 1.058 times the Ohio county-equivalent median of 436 square miles. It accounts for 1.1% of the combined county land area in the state.
See the complete Ohio ranking · What counts as a county equivalent?
Population and density of Montgomery County
The Census Bureau estimates that 539,598 people lived in Montgomery County on July 1, 2025. That ranks #136 of 3,222 county equivalents nationally and #4 of 88 in Ohio. Since the April 1, 2020 estimates base of 537,304, the population has grown by 2,294 (+0.4%), compared with +0.9% for Ohio as a whole.
With 461.4 square miles of land, that is 1,170 people per square mile (452 per km²), placing Montgomery County #155 nationally for density and #6 in Ohio. The median county equivalent has 47 people per square mile; the Ohio median is 120. Put another way, there are about 0.547 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 537,115 | 536,038 | 533,913 | 534,910 | 536,930 | 539,598 |
| Change | — | −1,077 | −2,125 | +997 | +2,020 | +2,668 |
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 Montgomery County
22 incorporated places lie at least partly in Montgomery County. Together they are home to 421,696 people (78.2%); the other 117,902 (21.8%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Dayton city, with 136,688 residents in the county (the city extends into 1 other county). Among places with at least 1,000 residents in 2020, Centerville city grew fastest since then (+4.2%).
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Dayton cityCounty seat · Also in 1 other county | 136,688 | −0.7% | 55.8 |
| Kettering cityAlso in 1 other county | 56,666 | −0.8% | 18.7 |
| Huber Heights cityAlso in 1 other county | 38,101 | +0.8% | 22.7 |
| Centerville cityAlso in 1 other county | 25,191 | +4.2% | 11 |
| Riverside city | 24,706 | +0.9% | 9.726 |
| Trotwood city | 23,190 | +0.5% | 30.5 |
| Miamisburg city | 20,414 | +2.4% | 12.3 |
| Vandalia city | 15,014 | −0.7% | 12.3 |
| Clayton city | 13,397 | +0.7% | 18.5 |
| Englewood city | 13,343 | −0.8% | 6.56 |
| West Carrollton city | 12,963 | −1% | 6.428 |
| Oakwood city | 9,441 | −1.3% | 2.195 |
| Union cityAlso in 1 other county | 7,134 | +4% | 8.489 |
| Moraine city | 6,627 | +3.1% | 9.282 |
| Brookville city | 5,999 | +0.1% | 4.237 |
Show the other 7 places
| Name | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Germantown city | 5,947 | +2.7% | 4.222 |
| New Lebanon village | 3,870 | +1.9% | 2.045 |
| Springboro cityAlso in 1 other county | 1,218 | +2.2% | 9.255 |
| Farmersville village | 1,006 | +3.2% | 0.715 |
| Phillipsburg village | 493 | +0.2% | 0.266 |
| Carlisle cityAlso in 1 other county | 221 | +0.5% | 3.559 |
| Verona villageAlso in 1 other county | 67 | 0% | 0.456 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Montgomery County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
Montgomery County is a central county of the Dayton-Kettering-Beavercreek, OH Metropolitan Statistical Area. Its 3 county equivalents have 826,554 residents on 1,281.6 square miles of land; Montgomery County accounts for 36% of the land and 65.3% of the residents. By combined land it ranks #243 of 393 metropolitan areas, and #77 by population. It belongs to the Dayton-Springfield-Kettering, OH Combined Statistical Area.
| County equivalent | Population 2025 | Land mi² |
|---|---|---|
| Montgomery County | 539,598 | 461.4 |
| Greene County | 174,322 | 413.6 |
| Miami County | 112,634 | 406.6 |
ZIP codes
42 ZIP Code Tabulation Areas have land in Montgomery County; 32 of them have most of their land inside the county, and the others mainly cover neighboring areas.
450054504245066453094531545322453254532745342453444534545354453714537745378453814540245403454044540545406454094541045414454154541645417454194542045423454244542645428454294543145432454394544045449454584545945469
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 Montgomery County
Montgomery County shares a land border with 7 county equivalents. It has more land than 5 of them. The largest neighbor is Darke County (598.1 mi²) and the smallest is Clark County (395.9 mi²). Together with its neighbors, Montgomery County forms a block of 3,567.7 mi² of land, of which it holds 12.9%.
| Bordering county equivalent | Land mi² | Size vs. Montgomery | Compare |
|---|---|---|---|
| Darke County | 598.1 | 1.3× larger | Compare |
| Butler County | 466.5 | about the same | Compare |
| Preble County | 424.2 | 1.1× smaller | Compare |
| Greene County | 413.6 | 1.1× smaller | Compare |
| Miami County | 406.6 | 1.1× smaller | Compare |
| Warren County | 401.4 | 1.1× smaller | Compare |
| Clark County | 395.9 | 1.2× smaller | Compare |
How big is Montgomery County compared with U.S. states?
Montgomery County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 2.2 times as much. Ohio’s county land could hold about 89 areas the size of Montgomery County.
Another way to picture it: the same land area would fill a square about 21.5 miles (34.6 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 Montgomery County?
Montgomery County has more land than 997 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 Montgomery County at #2,307 nationally by total area, 82 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% — 0.5 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 Montgomery County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #2224 | Wythe County, Virginia | 462 | Compare |
| #2225 | Montgomery County, Ohio | 461.4 | This county |
| #2226 | Lamoille County, Vermont | 461.3 | 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 39.753736, -84.290591. 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: 1,194,897,303 m²; AWATER: 7,492,173 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 Montgomery County?
Montgomery County, Ohio has 461.4 square miles (1,194.9 km²) of land and 2.893 square miles of water, for a total area of 464.2 square miles. It ranks #2225 of 3,222 U.S. county equivalents by land area.
Is Montgomery County the largest county in Ohio?
No. Montgomery County ranks #37 of 88 in Ohio by land area. The largest is Ashtabula County, with 702.4 square miles of land.
What counties border Montgomery County?
Montgomery County shares a land border with Preble County, Miami County, Greene County, Warren County, Butler County, Darke County, and Clark County.
What is the population of Montgomery County?
The Census Bureau estimates Montgomery County had 539,598 residents on July 1, 2025, ranking #136 of 3,222 county equivalents. That is 1,170 people per square mile of land.
What is the county seat of Montgomery County?
The county seat of Montgomery County is Dayton.
What cities and towns are in Montgomery County?
Montgomery County has 22 incorporated places. The most populous five are Dayton city, Kettering city, Huber Heights city, Centerville city, and Riverside city; 117,902 residents live outside any incorporated place.
Is Montgomery County part of a metropolitan area?
Yes. It is a central county of the Dayton-Kettering-Beavercreek, OH Metropolitan Statistical Area, which has 3 county equivalents and 826,554 residents.
How many ZIP codes are in Montgomery County?
42 ZIP Code Tabulation Areas have land in Montgomery County, and 32 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Montgomery County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 2.2 times as much land.
How many acres of land are in Montgomery County?
The land measurement converts to approximately 295,265 acres. Including water, total area is approximately 297,117 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.