County outline
Where Washtenaw County is located
Area breakdown
Land accounts for 97.7% of Washtenaw County’s measured area and water for 2.3%. Its combined area converts to 1,871.1 square kilometers or approximately 462,349 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 706.015 | 1,828.57 | 451,849.6 |
| Water | 16.406 | 42.491 | 10,499.8 |
| Total | 722.421 | 1,871.062 | 462,349.4 |
How Washtenaw County compares
By original Census land area, Washtenaw County ranks #27 of 83 in Michigan and #1309 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 1.243 times the Michigan county-equivalent median of 567.8 square miles. It accounts for 1.2% of the combined county land area in the state.
See the complete Michigan ranking · What counts as a county equivalent?
Population and density of Washtenaw County
The Census Bureau estimates that 370,214 people lived in Washtenaw County on July 1, 2025. That ranks #210 of 3,222 county equivalents nationally and #6 of 83 in Michigan. Since the April 1, 2020 estimates base of 372,265, the population has declined by 2,051 (−0.6%), compared with +0.5% for Michigan as a whole.
With 706 square miles of land, that is 524 people per square mile (202 per km²), placing Washtenaw County #326 nationally for density and #7 in Michigan. The median county equivalent has 47 people per square mile; the Michigan median is 62. Put another way, there are about 1.2 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 371,814 | 364,941 | 367,307 | 367,845 | 368,956 | 370,214 |
| Change | — | −6,873 | +2,366 | +538 | +1,111 | +1,258 |
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 Washtenaw County
Washtenaw County is divided into 26 municipalities and townships. In Michigan, county subdivisions are local governments, and together they cover all of the county’s land and residents.
The most populous is Ann Arbor city, with 122,233 residents (33% of the county). The largest by land is Sharon township, at 37.4 mi², or 5.3% of the county’s land. Among those with at least 1,000 residents in 2020, Saline township grew fastest since then (+20.5%).
| County subdivision | Population 2025 | Since 2020 | Land mi² | Share of county land |
|---|---|---|---|---|
| Ann Arbor cityCounty seat | 122,233 | −1.3% | 28.4 | 4% |
| Ypsilanti charter township | 53,721 | −3.5% | 30 | 4.2% |
| Pittsfield charter township | 40,265 | +2.9% | 27.1 | 3.8% |
| Ypsilanti city | 19,766 | −4.2% | 4.293 | 0.6% |
| Scio township | 18,597 | +6% | 32 | 4.5% |
| Superior charter township | 14,862 | +0.2% | 35.2 | 5% |
| York charter township | 9,130 | +0.2% | 34.7 | 4.9% |
| Saline city | 9,001 | +0.7% | 4.351 | 0.6% |
| Northfield township | 8,785 | +2.6% | 35.8 | 5.1% |
| Augusta charter township | 7,345 | +3.7% | 36.7 | 5.2% |
| Salem township | 6,786 | −3.3% | 34.3 | 4.9% |
| Dexter township | 6,510 | −2.8% | 30.3 | 4.3% |
| Webster township | 6,485 | −1.4% | 34.9 | 4.9% |
| Lodi township | 6,281 | −2.2% | 34.3 | 4.9% |
| Chelsea city | 5,424 | −0.6% | 3.687 | 0.5% |
Show the other 11 subdivisions
| Name | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Manchester township | 4,550 | −1.6% | 35.7 |
| Ann Arbor charter townshipCounty seat | 4,506 | −3% | 16.3 |
| Dexter city | 4,461 | −0.9% | 1.943 |
| Lima township | 4,215 | +4.7% | 34.5 |
| Milan city | 3,726 | −3.6% | 1.135 |
| Sylvan township | 3,545 | +6.9% | 32.6 |
| Saline township | 2,735 | +20.5% | 34.7 |
| Lyndon township | 2,662 | −0.2% | 32 |
| Sharon township | 1,774 | −2.5% | 37.4 |
| Bridgewater township | 1,551 | −4% | 36.2 |
| Freedom township | 1,298 | −2.4% | 35.4 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each subdivision inside Washtenaw County. Land: 2026 Census Gazetteer. How communities are listed.
Metropolitan area
Washtenaw County is a central county of the Ann Arbor, MI Metropolitan Statistical Area. Washtenaw County is the area’s only county equivalent, so the metro area has the same 706 square miles of land. By combined land it ranks #320 of 393 metropolitan areas, and #154 by population. It belongs to the Detroit-Warren-Ann Arbor, MI Combined Statistical Area.
ZIP codes
27 ZIP Code Tabulation Areas have land in Washtenaw County; 14 of them have most of their land inside the county, and the others mainly cover neighboring areas.
481034810448105481084810948111481184813048137481584816048167481684816948170481764817848189481904819148197481984922949236492404928549287
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 Washtenaw County
Washtenaw County shares a land border with 6 county equivalents. It has more land than 4 of them. The largest neighbor is Oakland County (867.4 mi²) and the smallest is Monroe County (549.4 mi²). Together with its neighbors, Washtenaw County forms a block of 4,751.5 mi² of land, of which it holds 14.9%.
| Bordering county equivalent | Land mi² | Size vs. Washtenaw | Compare |
|---|---|---|---|
| Oakland County | 867.4 | 1.2× larger | Compare |
| Lenawee County | 749.7 | 1.1× larger | Compare |
| Jackson County | 701.9 | about the same | Compare |
| Wayne County | 611.8 | 1.2× smaller | Compare |
| Livingston County | 565.3 | 1.2× smaller | Compare |
| Monroe County | 549.4 | 1.3× smaller | Compare |
How big is Washtenaw County compared with U.S. states?
Washtenaw County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.5 times as much. Michigan’s county land could hold about 80 areas the size of Washtenaw County.
Another way to picture it: the same land area would fill a square about 26.6 miles (42.8 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 Washtenaw County?
Washtenaw County has more land than 1,913 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 Washtenaw County at #1,350 nationally by total area, 41 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 2.3%, compared with a national county-equivalent median of 1.2% — 1.1 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 Washtenaw County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #1308 | Marshall County, Mississippi | 706.2 | Compare |
| #1309 | Washtenaw County, Michigan | 706 | This county |
| #1310 | Broome County, New York | 705.7 | 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 42.252217, -83.843423. 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: 1,828,571,104 m²; AWATER: 42,491,927 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 Washtenaw County?
Washtenaw County, Michigan has 706 square miles (1,828.6 km²) of land and 16.4 square miles of water, for a total area of 722.4 square miles. It ranks #1309 of 3,222 U.S. county equivalents by land area.
Is Washtenaw County the largest county in Michigan?
No. Washtenaw County ranks #27 of 83 in Michigan by land area. The largest is Marquette County, with 1,809.1 square miles of land.
What counties border Washtenaw County?
Washtenaw County shares a land border with Jackson County, Wayne County, Livingston County, Lenawee County, Monroe County, and Oakland County.
What is the population of Washtenaw County?
The Census Bureau estimates Washtenaw County had 370,214 residents on July 1, 2025, ranking #210 of 3,222 county equivalents. That is 524 people per square mile of land.
What is the county seat of Washtenaw County?
The county seat of Washtenaw County is Ann Arbor.
What cities and towns are in Washtenaw County?
Washtenaw County has 26 county subdivisions (cities, towns and townships). The most populous five are Ann Arbor city, Ypsilanti charter township, Pittsfield charter township, Ypsilanti city, and Scio township.
Is Washtenaw County part of a metropolitan area?
Yes. It is a central county of the Ann Arbor, MI Metropolitan Statistical Area.
How many ZIP codes are in Washtenaw County?
27 ZIP Code Tabulation Areas have land in Washtenaw County, and 14 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Washtenaw County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 1.5 times as much land.
How many acres of land are in Washtenaw County?
The land measurement converts to approximately 451,850 acres. Including water, total area is approximately 462,349 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.