Multnomah County was created on December 22, 1854. The county was named after the Multnomah Indians who were part of the Chinookan tribe that lived on the eastern tip of what is now Sauvie Island in the Columbia River. The first courthouse was built in 1866. Expanding county business required the addition of a north wing in 1885 and a south wing in 1889. In 1914 a new courthouse was completed.
The 1981 Legislative Assembly joined, county funded, Oregon's district and circuit courts into a unified state-funded court system. Effective January 1, 1983, the courts operate under the constitutional authority of the Oregon Judicial Department (OJD). Effective January 15, 1998, the legislature abolished the district courts, merged their judges and jurisdiction with the circuit courts to form a single, unified trial court level. Municipal, justice and county courts continue as limited jurisdiction tribunals outside of the state-funded court system and are not subject to its administrative control and oversight. There are 27 judicial districts, composed of one or more counties.