Founded in 1822 (boundaries declared) and 1826 (organised), Washtenaw County is one of 83 counties in the state of Michigan. Historically, Washtenaw County was formed from parts of Oakland County and Wayne County. The city of Ann Arbor is the county seat. With FIPS code of 161, Washtenaw County has a population of 369,390 and area of 723 square miles (1,873 km2).
List of all cities in Washtenaw County, MI alphabetically
| City/Town | Postal Code | Area Code |
| Ann Arbor, MI | 48103 | 734 |
| 48104 | 734 | |
| 48105 | 734 | |
| 48106 | 734 | |
| 48107 | 734 | |
| 48108 | 734 | |
| 48109 | 734 | |
| 48113 | 734 | |
| Barton Hills, MI | 48105 | 734 |
| Bridgewater, MI | 48115 | 734 |
| Chelsea, MI | 48118 | 734 |
| Delhi, MI | 48103 | 734 |
| Dexter, MI | 48130 | 734 |
| Dixboro, MI | 48105 | 734 |
| Dover, MI | 48130 | 734 |
| Four Mile Lake, MI | 48130 | 734 |
| Freedom Township, MI | 48118 | 734 |
| Hamburg, MI | 48189 | 734 |
| Hudson Mills, MI | 48130 | 734 |
| Lima Center, MI | 48118 | 734 |
| Loch Alpine, MI | 48103 | 734 |
| Lodi Township, MI | 48103 | 734 |
| Luce Township, MI | 48118 | 734 |
| Lyndon Township, MI | 48118 | 734 |
| Manchester, MI | 48158 | 734 |
| Northfield Township, MI | 48189 | 734 |
| Pittsfield Township, MI | 48104 | 734 |
| Podunk, MI | 48158 | 734 |
| Rawsonville, MI | 48197 | 734 |
| Salem, MI | 48175 | 810 |
| Saline, MI | 48115 | 734 |
| 48176 | 734 | |
| Scio, MI | 48130 | 734 |
| Scio Township, MI | 48103 | 734 |
| Sharon, MI | 48158 | 734 |
| Sharon Hollow, MI | 48158 | 734 |
| Superior Township, MI | 48105 | 734 |
| 48198 | 734 | |
| Sylvan Township, MI | 48118 | 734 |
| U of M, MI | 48109 | 734 |
| Webster, MI | 48130 | 734 |
| Whitmore Lake, MI | 48189 | 734 |
| Whittaker, MI | 48190 | 734 |
| Willis, MI | 48191 | 734 |
| Willow Run, MI | 48198 | 734 |
| Ypsilanti, MI | 48197 | 734 |
| 48198 | 734 |