The Tri-County Metropolitan Transportation District of Oregon (TriMet) is a transit agency that serves most of the Oregon part of the Portland metropolitan area. Created in 1969 by the Oregon legislature, the district replaced five private bus companies that operated in the three counties: Multnomah, Washington, and Clackamas. TriMet began operating a light rail system, MAX, in 1986, which has since been expanded to five lines that now cover 59.7 miles (96.1 km). It also operates the WES Commuter Rail line since 2009. It also provides the operators and maintenance personnel for the city of Portland-owned Portland Streetcar system. In 2023, the system had a ridership of 62,055,600, or about 196,900 per weekday as of the fourth quarter of 2023.

The Portland metropolitan area is a metro area with its core in the U.S. states of Oregon and Washington. It has 5 principal cities the largest being Portland, Oregon. The U.S. Office of Management and Budget (OMB) identifies it as the Portland–Vancouver–Hillsboro, OR–WA Metropolitan Statistical Area, a metropolitan statistical area used by the United States Census Bureau (USCB) and other entities. The OMB defines the area as comprising Clackamas, Columbia, Multnomah, Washington, and Yamhill Counties in Oregon, and Clark and Skamania Counties in Washington. The area had a population of 2,512,859 at the 2020 census, an increase of over 12% since 2010.