There are 36 counties in the U.S. State of Oregon.

The Oregon Constitution does not explicitly provide for county seats; Article VI, covering the "Administrative Department" of the state of Oregon, simply states that:

More details on the etymologies of Oregon county names and place names in general are documented in Oregon Geographic Names.

Oregon's postal abbreviation is OR and its FIPS state code is 41.The Federal Information Processing Standard (FIPS) code, which is used by the United States government to uniquely identify counties, is provided with each entry.

The FIPS code for each county links to census data for that county.