Washtenaw County is a county in Michigan, United States, in the southeastern part of the state along the Huron River between Detroit and Jackson. It had a population of 372,258 at the 2020 census and covers 722 square miles (1,870 km2), of which 706 square miles is land, centred near 42°15′N 83°50′W.
Ann Arbor is the county seat, home to the University of Michigan, and its postal code is 48103. The county has 7 cities, 1 village, 14 townships and one census-designated place. It sits in the Eastern time zone and carries FIPS code 26161.
Towns & Villages in Washtenaw County
Washtenaw County’s population concentrates around Ann Arbor and Ypsilanti in the east, with smaller cities spaced along the Huron and Raisin river valleys to the west and south.
| Place | Type | Township | Pop. | ZIP |
|---|---|---|---|---|
| Ann Arbor | City · seat | — | 123,851 | 48103 |
| Ypsilanti | City | — | — | — |
| Chelsea | City | — | — | — |
| Dexter | City | — | — | — |
| Manchester | City | — | — | — |
| Milan | City | — | — | — |
| Saline | City | — | — | — |
| Barton Hills | City | — | 316 | — |
| Whitmore Lake | CDP | Northfield | — | — |
| Dixboro | Unincorp. | Superior | — | — |
| Delhi Mills | Unincorp. | Ann Arbor | — | — |
| Geddes | Unincorp. | Ypsilanti | — | — |
| Mooreville | Unincorp. | York | — | — |
| Paint Creek | Unincorp. | Salem | — | — |
| Salem | Unincorp. | Salem | — | — |
| Stony Creek | Unincorp. | Augusta | — | — |
| Whittaker | Unincorp. | York | — | — |
| Willis | Unincorp. | Augusta | — | — |
Barton Hills, an incorporated village bordering Ann Arbor on the Huron River, is treated as a city-type municipality above for table purposes. Whitmore Lake straddles the Washtenaw–Livingston county line, and Milan straddles the Washtenaw–Monroe line; only the Washtenaw-side population is in scope here.
Townships
| Township | Pop. (2020) | Main settlements |
|---|---|---|
| Ann Arbor Charter Township | 4,673 | Delhi Mills, Foster |
| Augusta Charter Township | 7,083 | Willis, Stony Creek |
| Bridgewater Township | 1,615 | Bridgewater, Sharon Hollow area |
| Pittsfield Charter Township | — | Southern Ann Arbor suburbs |
| Superior Charter Township | — | Dixboro |
| York Charter Township | — | Milan area, Mooreville |
| Ypsilanti Charter Township | — | Rawsonville, Willow Run area |
| Dexter Township | — | Dexter area, Hudson Mills |
| Freedom Township | — | Rural, no major village |
| Lima Township | — | Lima Center |
| Lodi Township | — | Saline area |
| Lyndon Township | — | Lyndon Center |
| Manchester Township | — | Manchester area |
| Northfield Township | — | Whitmore Lake |
| Salem Township | — | Salem, Paint Creek |
| Saline Township | — | Saline area |
| Scio Township | — | Scio, western Ann Arbor suburbs |
| Sharon Township | — | Sharon Hollow |
| Sylvan Township | — | Chelsea area |
| Webster Township | — | Webster area |
ZIP Codes
- 48103 — Ann Arbor (also serves Delhi Mills and western county areas)
Only Ann Arbor’s ZIP code is independently confirmed for this profile; other cities and townships each carry their own postal code, unverified here, and readers should check the U.S. Postal Service ZIP lookup for the exact code that serves a given street address.
Geography
Washtenaw County lies on the glaciated plain of southeastern Michigan, drained by the Huron River, which runs west to east through Dexter, Ann Arbor and Ypsilanti, and by the River Raisin in the southwest corner. The terrain is gently rolling farmland and woodland interspersed with kettle lakes, with 16 square miles of the county’s area under water. Bordering counties are Livingston to the north, Oakland to the northeast, Wayne to the east, Monroe to the southeast, Lenawee to the southwest, Jackson to the west and Ingham to the northwest.
Demographics
Washtenaw County had 372,258 residents at the 2020 census, with a 2025 estimate of 370,214. Ann Arbor and Ypsilanti are the two largest communities, with Ann Arbor alone home to 123,851 people. The county’s median household income is $83,754, well above the Michigan state figure of $69,183. With 706 square miles of land, the county’s overall density works out to roughly 528 people per square mile, concentrated heavily in the Ann Arbor–Ypsilanti corridor.
Economy & Local Life
Higher education and health care dominate the county economy. The University of Michigan is by far the largest employer, with 35,446 workers, followed by Trinity Health at 7,435 and the federal government at 3,060. Outlying cities such as Chelsea, Dexter, Saline and Manchester retain smaller manufacturing and agricultural-service bases. The county’s best-known annual event is the Ann Arbor Art Fair, held each July.
History
Washtenaw County was authorized by territorial legislation in 1822 and organized as a county in 1826. Its name comes from an Ojibwe word meaning “far away waters,” a reference to the Grand River watershed near the county’s original boundary description. Ann Arbor was platted in the 1820s and became the county seat; the University of Michigan relocated there from Detroit in 1837, the same year Michigan achieved statehood.
Getting There
Interstate 94 crosses the county east–west through Ypsilanti and Ann Arbor, with US-23 running north–south along the county’s eastern side.
- Detroit — 40 miles east
- Jackson — 35 miles west
- Lansing — 55 miles northwest
- Toledo, Ohio — 50 miles south
Detroit Metropolitan Airport, about 25 miles east, is the nearest major commercial airport; Ann Arbor’s own municipal airport handles general aviation only. Amtrak’s Wolverine service stops at the Ann Arbor station on its Chicago–Detroit route.
Frequently Asked Questions
What is the Ann Arbor postcode?
48103 is Ann Arbor’s primary ZIP code, though the city uses several ZIP codes in total.
What county is Ann Arbor in?
Ann Arbor is the seat of Washtenaw County, Michigan.
How big is Washtenaw County?
Washtenaw County covers 722 square miles (1,870 km2), including 16 square miles of water.
What is the population of Washtenaw County?
Washtenaw County had a population of 372,258 at the 2020 census, with a 2025 estimate of 370,214.
What is the largest city in Washtenaw County?
Ann Arbor, the county seat and home to the University of Michigan, is the largest city with 123,851 residents in 2020.
Where did the name Washtenaw come from?
The name derives from an Ojibwe term meaning “far away waters,” referring to the Grand River watershed near the original county boundary.
What counties border Washtenaw County?
Livingston, Oakland, Wayne, Monroe, Lenawee, Jackson and Ingham counties all border Washtenaw County.
More counties in this state: Towns and villages in Michigan.