Founded in 1843, Washington County is one of 36 counties in the state of Oregon. Historically, Washington County was one of the original four districts of the Oregon Country (as Twality District). The city of Hillsboro is the county seat. With FIPS code of 67, Washington County has a population of 600,811 and area of 724 square miles (1,875 km2).
List of all cities in Washington County, OR alphabetically
| City/Town | Postal Code | Area Code |
| Aloha, OR | 97006 | 503/971 |
| 97007 | 503/971 | |
| Banks, OR | 97106 | 503/971 |
| 97109 | 503/971 | |
| 97125 | 503/971 | |
| Beaverton, OR | 97005 | 503/971 |
| 97006 | 503/971 | |
| 97007 | 503/971 | |
| 97008 | 503/971 | |
| 97075 | 503/971 | |
| 97076 | 503/971 | |
| 97077 | 503/971 | |
| Buxton, OR | 97109 | 503/971 |
| Cedar Mill, OR | 97229 | 503/971 |
| 97291 | 503/971 | |
| Cornelius, OR | 97113 | 503/971 |
| 97123 | 503/971 | |
| Durham, OR | 97224 | 503/971 |
| Forest Grove, OR | 97116 | 503/971 |
| Forest Heights, OR | 97229 | 503/971 |
| Gales Creek, OR | 97117 | 503/971 |
| Gaston, OR | 97119 | 503/971 |
| Glenwood, OR | 97116 | 503/971 |
| Helvetia, OR | 97124 | 503/971 |
| Hillsboro, OR | 97006 | 503/971 |
| 97007 | 503/971 | |
| 97123 | 503/971 | |
| 97124 | 503/971 | |
| King City, OR | 97224 | 503/971 |
| Manning, OR | 97125 | 503/971 |
| North Plns, OR | 97133 | 503/971 |
| Orenco, OR | 97123 | 503/971 |
| 97124 | 503/971 | |
| Portland, OR | 97223 | 503/971 |
| 97224 | 503/971 | |
| 97225 | 503/971 | |
| 97229 | 503/971 | |
| 97281 | 503/971 | |
| 97291 | 503/971 | |
| 97298 | 503/971 | |
| Progress, OR | 97005 | 503/971 |
| Rock Creek, OR | 97229 | 503/971 |
| Scholls, OR | 97123 | 503/971 |
| Sherwood, OR | 97140 | 503/971 |
| Tektronix, OR | 97077 | 503/971 |
| Tigard, OR | 97223 | 503/971 |
| 97224 | 503/971 | |
| 97281 | 503/971 | |
| Timber, OR | 97144 | 503/971 |
| Tualatin, OR | 97062 | 503/971 |
| Verboort, OR | 97116 | 503/971 |
| West Slope, OR | 97225 | 503/971 |
| West Union, OR | 97124 | 503/971 |